what is requirerd in swapping in a a12/a14/a15 in a 1k 2-door? can the stock gearbox be used??

Depending on engine, it requires the normal mount bracket swap. You can use the stock gearbox but you need to use the A10 flywheel. And A12 stock aircleaner hits the bonnet but can be made to fit, but i think A14 and 15 need a different cleaner.

If you use an engine setup like dodgeman is doing early a12 block with a12a rods, a14 crank and a15 pistons then the stock mounts and alternator postition can be used and as stated use the a10 flywheel and maybe a pressure plate with a little more clamping force along with a HD aiken clutch. Youd want to change the diff ratio to 3.9 or get a diff with a 3.5 or 3.7 for better cruising otherwise the extra revs of the longer stroke will buzz or hum you to nuts.

The simplest engine swap is to use the 1200 engine from a '70 to '73 Datsun 1200 car. The engine is a direct bolt in swap to your chassis. If you use the 1000 altenator, then all the electrics will connect right up too, but you will need to remove & re-use the studs that hold the altenator bracket from your block.
If you use any of the later engines, you will need to modify engine mount brackets & the altenator wiring, as the altenator will be on the wrong side of the engine.

If i remember rightly, after all, it was more than 20 years ago, i used the 1200 engine [as distinct from the later, '74 & up, A12 engine] with a modified A10 flywheel that had been drilled for the larger A12/14 clutch. This fitted & worked inside my original 1000 gearbox after i managed to fit the 1200 clutch release bearing & carrier to the 1000 clutch fork.

The only reason that this box was later replaced is because i had bought the five speed.

The A10 flywheel has a groove machined around the outside of the original, small diameter, clutch plate, so we machined the face of the fluwheel down to the base of the groove, untill it was flat, then redrilled it for the larger clutch. We also machined a little from the cylinder block side of the flywheel for weight reduction. The A10 flywheel is the lightest of the A series flywheels anyway, so it didnt take much to trim it down to a good weight, although i forget what the actual weight was. [I will weigh it later, as i plan to re-use it]

Use the diff center from a 1200 car for a direct bolt-in 3.9 ratio, or use the 3,7 ratio from a late 310 Sunny wagon. You will need to find one that had the A15 factory fitted from new in order to get the 3.7 to 1 ratio. This car used the larger H150 diferential, & despite some claims to the contrary, it would seem that you would need a spacer ring, & an extra gasket, to space the H150 diff foward a little to allow the axles to align correctly.

How much does it need to be spaced foward? Ahhhh, therein lies the $64,000 question. Pitroad in Japan claim to know, as they have an adapter /spacer ring for sale to allow this conversion, but they are not advertising this important dimension.

All the A series engines after the A10 were taller in the block & if you use the original carb & air cleaner, it will rub underneath the bonnet. The best fix is to use semi side draught carbs [GX setup or SU] Side draught carb[s] [Webber etc] or factory EFI [if you can find one] All of these clear the bonnet with ease & provide a performance boost when correctly tuned.

I hope that this is of some help.

By the way, could you let us know which country you are in? Filling in some of your details can help us provide you with a better quality of help as some advice is specific to various countries or regions.

does the accelerator cable and fuel lines line-up? and is there any major differemce between the 1k 4speed and the 1200 4speed??

the 1200 4 speed is a little better but the 60a is even better again if you can make a custom mount for it. However depends on your driving as I found the standard 4 speed on the K was fine for me with a mild a15 which chirped even on 3rd gear with the 4.11 diff. It was wise though for me to get an overdrive for it though made big difference in top end.

When i converted my coupe to an A14 i used a 1200 box, and a 1200 clutch cable. You have to massage the tunnel to fit the clutch fork in, and redrill the firewall to hold the cable mount. Not too much involved, and i think it ends up better so if you snap one they are easier to get ahold of.

I never had the "clutch arm in the firewall" problem because i used the modified A10 flywheel, so i had forgotten about it.
Using the modified A10 flywheel allowed the clutch to sit closer to the block, which is probably why i was able to get it into the A10 bellhousing.

When i switched to the five speed, the clutch release arm also sat further foward so that the bearing could reach the fingers. This, along with two flat washers between the gearbox crossmember & the chassis [to allow the gearbox to fit without tunnel mods.] gave me just enough clearance to make it all work.

This time, i will engineer it properly.

doesnt seem to hard, although i will be going the easy path ( early a12, original 4speed) anyways what brakes is suitible for a midly modded a12?? Im after something like the Sigma conversion, is this hard? is there any other alternative (besides 1200 brakes and expensive kits)?? and whats this i heard about 1200 rear drums?? (i know theres alot to answer to

1000's used a diferent drum on the rears. They aparently did not use a supporting rib around them, but the fronts did. These front drums were used on all four corners of the 1200, so if nothing else, it simplified the parts situation as the parts dept needed only one drum to service everything on a B10 or B110.

If you have the originals on the rear, then use the displaced front drums on the rear when you switch to discs.

As for so called "expensive" kits, just remember, great brakes will save your car, perhaps even your life when a $3,000 engine wont. Now, whats that worth to you.
I bought the full kit new, & i believe it was worth every cent.
In fact, if it came down to a tight budget, i would run the good brakes & the stock 1000 engine, rather than the hot engine & the stock brakes. I can fit the engine later.