Some twenty years ago my neighbor's friend let his 60's era 120 engine freeze. They did a complete re-power and I bought the old engine and drive for parts. Left over is the "leg" {unmolested). I will be in Banks, Oregon on the 13th of August. Meet me there with two six packs of Widmer's Hefe...
Scott, I would also be interested in seeing what your pistons look like.
I would especially like to see the pistons in Quenchmaster Rick's 5.7s. Probably OEM deep dish.
Here is one of mine, not OEM.
If what you state is true "so shaft turns,but no water pump or gears" and you have a drive earlier than an Alpha, your lower unit input shaft may be sheared off at the "O" ring groove (not uncommon).
The only new replacement springs that I found that were compatible. Available here and in limited quantity.
https://www.marineengine.com/parts/omc-parts/omc-boat-parts.php?year=1987&hp=5.7&model=574AMFTC&manufacturer=OMC+Stern+Drive§ion=Distributor+-+Prestolite+Ibm-7013c
Originals...
I have gone ahead and had an adapter made up. My engine did not come with a raw water pump, It was delivered to be supplied by the outdrive's pump, not adequate for a full closed system. The crankshaft option with the Johnson pump is slightly less expensive than rounding up a belt driven...