Difference between 1 and 2 piece rear main seal flexplate/engine coupler

[85Nova2]

So I've decided to build 2 fresh engines for my Nova 2, a friend of mine has 2 really nice 350 blocks for sale that are 2 piece rear main seal. The boat currently has 1 piece rear main seal blocks. Will I need to change anything for the engine coupler? Thank you.

 

[Bondo]

Ayuh,.... Welcome Aboard,.... That depends on whether yer couplers bolt to the crankshaft, or the flywheel,....

If they bolt to the flywheel, the new flywheel oughta have the same coupler bolt pattern,....
with a smaller crankshaft bolt pattern,...