Hi Scott
You have added another thing to list of things to check on stuck engine, think this one falls under check the simple stuff first, but who would have thunk of engine won't turn because the transmission or flywheel is stuck.
Yes the critters love to climb into the bellhousing and build nests. Years ago my HUPs clutch suddenly started slipping, one weekend to the next, pull the transmission and discovered evidence of a mouse nest splattered all over the inside of the housing, but the real problem was there was mouse nest material wedged in at the fulcrum of the clutch fingers. What I surmise was that when I pushed the clutch in to start the engine the mouse nest was thrown outward and some of it wedged there, causing the clutch to slip.
Which type of engine stand were you thinking about? I made test stand for the Chev engine that has proved so useful that I now have 4 or 5 of them sitting around with engines on them. If your interested take a look at evolution of the test stand at
http://canadianmilitarypattern.com/EngineTesting.htm I made the stand so it could also handle flat head V8s.
Keep us posted on your progress, great to hear the engine is free and turning.
Cheers Phil