Wow, lots of variables here,
First off, does it run?
Now, obtain a factory service manual, you will need it...
When doing a compression check, you need to use the type of tool that screws into and seals in the spakplug hole, not a hand held one with a rubber tip.
You also need to hold the throttle wide open during the compression check.. if numbers are low, pour a tablespoon of thin oil, or kerosesne, in each cylinder, spin the engine, and recheck compressions.
As for turning the engine over by hand, with the stator nut, if all the plugs are out it is no problem.... don't try it with the plugs installed tho.
Check first thing, to see if it was hydrolocked, and has bent rods, see the sticky thread above this, for the method... determine if this was actually wy it was seized up...
As for swapping parts from a different engine, yeah, you can do top end, but if you need to do rods also, not so much, as differences in crankshaft bearings may necessistate engine removal and determination as to if a Swap can be made.
If the top end was never disassembled, there is no need to mess with the timing and cam chain, simply verify correct valve adjustments.
Sitting as long as it has, dump all the fuel, and clean the gastank, even tho it was coated prior, remove all the old fuel...if the p/o did the por15 treatment, no telling how long he let it dry before fueling it, and that causes issues with carbs also.
Like I say, lots of stuff to accomplish beforehand...