440/4 speed install, which method?

I like to assemble outside and install as a unit.
Installing the assembly from the top has drawbacks as noted above. If you have a deep oil pan on your 440, it eats up the clearance between the K-member and firewall. You'll understand what "shoehorn" in A-body terms means afterwards. It helps to lift the rear of the vehicle.
Best way, I'll agree, is install the assembly from the underneath with K-frame.
Either case you need to be exact on the mounts to get the assembly in and positioned where it belongs.