I'm the other way around.....If the transmission doesn't need any work, I'd leave it in place. Having done hundreds of them over the years I don't usually have any trouble getting the clutch splines lined up. Stick the tranny in gear and rock the crank back and forth with slight pressure pushing the engine toward the firewall. If you hung the engine square with the bell housing, it should slide right in. Depending on year, body style, and engine, sometime I leave the exhaust manifolds on, sometimes I pull them first. '64-76 V8A bodies ....I always pull the LH manifold. '68-70 340 cars.....I always pull both so there is no chance of breaking one. Most B and E bodies....I leave them on. Sometime on an HP big block B or E I'll pull one or both depending on what the clearance looks like and if it has PS or not. I usually pull headers loose from the motor but I leave them wired to the inner fenders unless they're an odd brand that gets in the way of something.
The sandwhich mounts don't interchange with the spool mounts....takes a different K-member.