i've done several CB450's, 500T's, Yam TX500's, XS's, all the way to a GS1000 alone. at 57, this may just be a bad idea, but there is never anyone around. wives don't really appreciate lifting motors so they don't count...
i've never tried the lay the frame over the motor approach because i always build a rolling chassis first. i consider it a better order to get all frame, wheel and suspension mods sorted out without the weight of the motor in frame.
bike is clamped/tied to bench as per pic (gas tank removed). wrap your frame in used padded packing envelopes or similar and use masking tape as required. test any tape on your fresh paint for any peel up etc and remove it right after motor is in. almost impossible not to nick frame somewhere, btw...
if you have a little plywood platform about the same height as lower frame rails it's very helpful to set motor on so install is more a two step thing. pre-plan your moves with all bolts nuts and plates laid out correctly. a piece of board and car scissor jack underneath works ok for "fine" adjustment to get a first bolt through, the rest are easier.
not a pleasant process but doable.