If you are using A14 pistons, in an A12 block, with the A12 crank, you will need A12 rods with the larger wrist pin hole. This can be done by

A. Boring the A12 rods
B. Using the A12a rods
C. Using A13 rods [the 76mm bore version.]

If you are using A15 pistons in an A12 block with an A14 crank, you will need A12 rods with the larger wrist pin hole. This can be done by

A. Boring the A12 rods
B. Using the A12a rods
C. Using A13 rods [The 76mm bore version.]

There is no reason to assume that one engine would be any more reliable than the other, although the longer stroke engine would develop more torque, so would need less flogging to return a given level of performance & the lesser flogged engine should live longer. At least, thats my version of the story.

as per demojobs post for the modded a12 block ages ago, ive collected all the necessary partsfor the new leagal a12 big block conversion (a14 crank a15 pistons and head).
reading the classifieds, the a12 with the a14 pistons sseems aeasier and more reliable.
would all that had to be machined be the wrist pins on the conrods and the block bored?
this is all in a post 73 a series block.
1200rc is also interested on this one for the rc.