The benefits.
A. It allows me to install an engine of up to 1434cc without any structural mods to engine mounts at all as the 1200 block is a pure 'drop in'.
B. By using the 1200 block [with an A12 engine No. prefix] it reduces engineering approval dramas.

The parts.
Desireably, you would use rods from an A12A, or the short stroke version of the A13, but these are hard to get. The alternative is to have your A12 rods bored in the small end to take the larger wrist pin from the 76mm[+] pistons.
You will need pistons from the A15 engine as these are shorter in the crown height & should rise to be flush with the deck.
EDIT the pistons will need a small amount machined from the crown. Possibly .5mm.

The finished product will look like a "factory" built car [no home grown engineering] while boasting a sneaky 23% boost in capacity [from 1171cc to 1434cc] & it's ALL done with standard Datsun parts. The crank & pistons are the only modified parts, & surely a simple lathe job hardly counts as "modified"

I will post pics of my progress as i go along.

The stock A14 crank does not touch the 1200 block anywhere, the machining is done to ensure that it doesn't touch the bottom of the pistons when they are at BDC. You really need to ensure that the counterweights clear as the piston is at the top when the crankpin swings by. The simplest method of cleaning up the small amount of material that needs to be removed is to chuck it in a lathe. This process also removes a small amount from the web near the crankpin, which does no harm, but if you could find a way to clean up the counterweight without touching the crankpin side, then that would work as well.

I like the sneaky aspect of this engine as most would see it as just another dinky 1200 engine with twin SU's. Little do they know what lurks within,...Ahh-hahahahahaha