The trans mount is rubber, and the driveshaft is fixed by rubber flex discs and a rubber center support - it will take SOME flexing, but not a whole lot, as you can obviously damage the mounts if they are moved too far. FWIW, the engine mount R&R procedure doesn't call for disconnecting the tranny mount or disconnecting the driveshaft, so you should be able to lift the engine at least enough to get the mounts off without too much concern.