I think the 1200 gearbox will go first thats if you are using the A12 gear box not the A14 smooth case box as that is stronger.
I Have a locker (mig welded centre) in 1200 sedan. i think they are great. Only prob is when i first got it with a shell i got for free the guy had blown the pinion out of the casing (alloy casing). I then took the crown wheel off it and matched a crown and pinion from a steel casing and put it in that. Next problem since then is it has been through 3 axles 1 tailshaft and recently destroyed a pinion which destroyed the crown. Now all changed over into a alloy casing now as that is all i had left at home so the centre is very strong! Thats a standard 1200 centre! i have pics and will put them on this site when i can.
The reason my gearbox hasn't blown is that it is a A series 5 speed mean't to cope with the A15.

The vannett diff would be a lot stronger and i think you will have a fair bit of trouble breaking a welded center (as long as it is done properly) and the axels are a bigger so that should be no worries. Bigger uni joints in the tail shaft would be recommended maybe out of a bluebird, but from my experience i say the gearbox will go first and i will pick 2nd gear to stuff up first.

I agree, it's gonna be the gearbox that goes next. Stock A12 4 speeds are SO weak, the first power shift or high rpm launch you do and you actually hook up, it's going to asplode. That's my bet

i have a feeling it may be the clutch or fly wheel again, that gear box has taken a beating and still continues to go......
eiter that or the seal on the carby box when it finally gets a full dose of boost

hehe, fun fun

well it's gonna be a little while before i get her on the road again, but we will soon find out

gearbox

From personal experience, I was a hoon years ago too, I reckon it will be 2nd gear that will break first too. I remember killing 2 gearboxes in 1 day after some serious tarmac circlework one Christmas.

My 2 cents is on further gutter rash??

Axle

Dattodude is on the money. When my CA18DET ute was first running a welded 1200 diff, the axle lasted two weeks before snapping at the diff centre. As mentioned its a scary feeling when they let go as the car drifts all over the road.

i very much doubt that it will be the diff that goes first being a H190, i ran a H165 locked in a bluebird and it lasted bout 9months before snapping an axle.
my money is on the box going first, youll pull second gear out if you change hard enough
good luck to you and i hope you all the fun in the world with your locker

The only way an axle will snap is if you get traction, in my FJ20T ute it had a stock and locked diff which had no problems till i ran at eastern creek where its a lot sticker than the street and it snap on a 6000rpm launch.
My mates own a CA18DET which makes bout 220hp at the wheels and has been running the same locked ute diff for 3 years now just because the car never has any traction to snap anything.

your diff want go its welded the only thing that will happens to that is you my snap you welds depending on how you locked my has plates and all in there .
Cheers Luke