I just support the engine (usually with a pantograph jack but if the bike is on a lift it can be left dangling by the front mount and top link and wiggled easily with a small pry bar if needed), and pull the primary and transmission. Not sure why anyone finds it difficult. and I certainly do not pull the guts out of the gearbox or snatch the engine because the shafts don't get in the way of anything.
Pull starter, primary, swingarm, remove two bolts holding gearbox to engine mount, done. The case can't come out from the bottom because of the crossmembers but they do come out the left side. I installed the deeper (because it's got an oil pan) later bagger box the same way (after removing the crossmembers of course) and that was painless too.
How does anyone manage to make it difficult?? I've done it with tapered and splined gearboxes without a second thought and if it was difficult I'd find a way that wasn't because I'm lazy.
One other way I just did for grins (because it looked interesting in a Featherbed-framed Sportster build) was to stuff the engine on the floor then lift the frame with cargo straps as slings (I have a bad back so no lifting engines for me at all) to midair and finish the trans and swingarm install with nothing below the motorcycle except a pantograph jack to manipulate the gearbox. It worked great and I recommend it to all cripples like myself. I don't find the engine an obstacle at all either way but one cool thing about slinging the frame is you cannot possibly tip the machine over and the other is it's easy to roll the engine into the frame on the floor (pad frame rail to protect the paint) without lifting it.