Will the pistons go up far enough in the block to get the crankshaft out without having to tear the motor down. A family friend has one with 50K on it and it might have a crank problem. I think it has a rod knock.

if it has rod knock, the rod that has the spun bearing will have to be changed. you will also have to pull the transmission to get the crank out and raise the engine. Might as well pull the motor out and go through it the right way instead of jerry rigging it.

I changed a crank in a 350 like that once ... make sure all the valve are closed before attempting .

Maybe but I don't think so.Last crank pin is out of sync.Do it right and besides the rods will need reconditioning (with new bolts) if one spun.

There are no spun rod bearings. It has a little rod knock on start up and its a farm truck that they do not want to throw tons of money at. They thought that if you could put a crank kit in it for a few hundred they would.

If it's a farm truck and only knocks on start-up I wouldn't mess with it. In case of failure those engines are cheap cuz' nobody wants 'em.

only on startup could be piston slap or lifter not pumped up,

Sometimes rolling in a new set of bearings will take care of that type of problem. You should be able to do that with pan off. More than that, I'd pull the engine.