Helped a friend of mine stuff a Ford GT500 (5.8L supercharged) engine into his Cobra. Never again.
Not enough room to drop in the engine/transmission as an assembly. Not enough room to install either the engine or the transmission separately. Could not go from the bottom, engine too wide for the frame rails. Could not tilt the engine and slide in the transmission as the heads were would hit the firewall.
So, we cut the floorboard out of the car, installed the engine and transmission, then welded the floorboard back in. If he needs to remove either, he will have to do it again. As the floorboard is integral to the integrity of the body structure, it had to be welded in.
Oh, did I mention, we had to do it again because the numbskull forgot to install the clutch disc before we put it all back together again?