OK, it's apparent that you haven't played with too many of these, so i will add what little i can to make it simplified.

The rods are the same length as standard 1200 /A12 ones, with the exception of the larger wrist pin eye. My existing 1200 GX engine uses A14 pistons with the little end opened out to take the larger pin. This time i elected to go with a factory stock part. A13 [big bore version] & A12a rods are dimentionally interchangeable

The A14 crank will fit the 1200 /A12 block without alteration. There is quite enough room in the blocks that we tried.
The lathe work was't to allow the crank to fit the block, but to ensure that the counterweights miss the bottom of the pistons when the pistons are at BDC.

Could you do the necessary mods to the crank with an angle grinder? Hell yes, you could do it with a hand file if you were really really patient, but i seriously question why you would have an angle grinder in your engine assembly area. Is this the best engine work that you can do?
The the only part that actually needs work is the small part of the counterweight that would intefere with the piston. The best way to check this is to simply assemble an old A12 rod & piston onto the crank [with a suitable bearing] & rotate it around the journal. Then grind away the part where it interferes. Repeat for the other three journals.
Even a blacksmith could do that. That's all the dummy fitment that was required in the first engine, so we can put that small fortune back into our pockets. Wasn't that simple?

Balancing is always done on all my engines as a standard procedure, so what's the problem here? Don't you balance yours?
The A15 pistons should rise to be almost flush with the block, so this is not a special part of the build. Just standard rebuild stuff here. The A15 pistons were selected because they are shorter in the pin to crown measurement & a dummy trial fitup showed that it would work, so the first engine was built from leftovers.

For me, saving money on a cost effective & very practical A14 transplant is not the prime objective here, although it could, & probably should be for many,... geting the combination of parts that i want IS the prime objective.
I try to save money by using what little skills i have gathered after almost 40 years as a mechanic, & by doing as much as i can myself.

Now you seem to have overlooked the fact that i have not asked, nor even suggested that you,... or anyone else for that matter, should duplicate this engine, nor do i suggest that anyone should spend money on having engineers build engines for them un-necessarily, only you are suggesting this.

It's an exercise that will cost ME about the same as a regular "improved performance" engine buildup & will take roughly the same investment in time, effort & other resources. Since i am not looking for ultimate performance, the points that you labour upon, like rod angle & the alleged reduction in "mechanical efficiency", along with this reduction in sensitivity to valve timing [whatever that's supposed to mean] are all rather moot.

We have one of these engines running here in a 1200 coupe already & after more than a year of flogging, it still runs strongly. Mine will be in a milder state of tune & I expect that it will serve me well in its intended role.

If it doesn't work, then i will know why from first hand experience, instead of coming up with a great confection of rhetoric revolving around some airy fairy theories about "reduced volumetric efficiency" based on nothing more than a foundation of "I reckon"

You seem to be obsessed with absolute minimal costs & blacksmith engineering, & for a low cost project, i'm sure that this approach would be fine for you, but for me, this car is a plaything & i want to do as good a job as i can. Quality is always appreciated, & it's all fun.

The criteria for its existance?
No visible or un-necessary home grown engineering
To make the finished product appear to be a factory built car if possible
To assemble a maximum capacity engine for this car built from readily available standard Datsun /Nissan parts, & based on core components already on hand, with a minimum of special engineering.

I'll be sure to let you know how it runs.
The End