Doing an engine swap 5,7 - 5.7. Seemed simple enough until the flywheel on the replacement engine is smaller than the old motor.
Also the coupler (alpha) will not align (the coupler it is the three prong style) and is bigger than the flywheel.
Cannot swap flywheels because of center hole size difference. What do i need??
Thanks in advance.

Sounds like one motor is a 2 piece rear main and the other is a 1 piece, is this the case?

They each have their own style fly wheel and 2 size flywheels for each type available. Coupler will fit, although the larger coupler will not clear the older 2 piece style bell house for which they make a retro fit coupler. Also starter has to match the size of the flywheel.

If you explain what you have, I could tell you what you need as I have done them before.

Mr. Maine,
The motor being removed, BAD, has Merc S/N J192822 it has a composite timing cover so I assume it is Vortec. This motor has a larger flywheel and smaller center hole.
The replacement motor has a Merc# on the water pump boss of V0103FRD. it has the smaller flywheel and bigger hole.
We have starters for both. Only have the bell housing and coupler (too large to clear smaller flywheel) from removed motor (vortec?).
You mentioned a retro coupler. Any idea where to get one new or used ok. Part#.
I hope that makes sense!
Thank you for your help,

Does the motor you are putting in have a counter weight where the flyweel bolts? If so, you need a 14 inch flywheel (168 tooth) for a 2 piece block and everything else should work.

http://www.summitracing.com/parts/zzz-50-6504/overview/

That should be the one you need if what you are describing is correct.

Thank you Mr. Maine.
Problem resolved, pending start-up, Wednesday.
Thanks again.