If you must install an engine/trans assembly from the top, consider lifting the rear of the car to help cut down the angle. Possibly fab a thin guard that is taller than the top edge of the core support and another for the firewall? Maybe install the crank pulley after the assembly is in?
Wow! Now, I've pulled the Valve stems, to drop the front.. but Man, that's thinking Outside the Box! I'll remember that as long as I live! Thank You! ( not that this applies to me, But Knowledge is Power!)