I cant agree or disagree as I haven't installed an engine separately w/o the trans in decades. I can attest to trying to stab the the trans into the motor when they are both suspended and , the conclusion is that method sucks a*& but, if you have the patience, you can make anything work. To me(pea brain) Just makes the most sense to use the @RUSH55 suggestion to mount the motor first, then use the trans Jack w/ the drive shaft disconnected to stab it. reducing one moving variable seems like the most logical approach unless of course your interior is apart then you can use more detailed engineering like what @Pighead suggested.
Hoping at some point to be posting q's of easier challenges.. my .02