The stock rods are forged, the H-Beam rods are forged and structurally stronger due to mostly their profile and perhaps to their material composition.

I wouldn't worry about the rod ends. If it is a worry get them shot peened after honing them.

Quote:
Bore the small ends of the normal A12 rods to 19.7mm and call them A12A rods.

WHOA, you even converted it to a LWB.

It isn't an additional port for a cold preheat plug? Used in cold climates to de-ice the block coolant?

Regarding the 'extra' on the M2 It looks like another threaded port into the side of the block.

I'm not too sure about the validity of the M2 block containing a lighter, scalloped crank, I have come across many with just the normal crank.

Would you happen to have a picture of the A12 M2 crankshaft in your engine?

J15 is very heavy and not much more powerful only 6hp more. Also not many performance parts available.

A15 is much better and an easier swap. It will give extra 10hp and you can modify it to produce much more power.

Nissan J Engine

Nissan A Engine

Watch your clearances to the strut tower, things will be just about close enough as is without using a spacer or adapter plate.

Here are some more 'ideas'.

Sure Dave.

Try search 'Datsun A12 Distributor'

And, voila first, second and third on the search results.

Go the H165 first. If blow up. Change.