Have just about got the engine in the right place. Just need to machine some bushings for the swingarm, then I'll be able to do the final clearancing and cut some gussets to weld into places where I've weakened the frame. Took a few pics to show how I test-fit the engine, mark-up the frame, and then clearance a little bit at a time.
Also slid the engine cradle tubes back into place to see how they fit and it's very
close. Think I could probably just barely almost have made it work without cutting out the engine cradle. But I wouldn't have known that without doing it this way, and more importantly, I couldn't physically fit the engine into the frame with the engine cradle in place. So as I see it now, I've got three options:
1) Bend-up some new tubes and weld them into place. Easy enough. But the main clearance problem is the oil drain bolt, which I'd still have to notch the left engine cradle tube to clear. Would most likely just pierce the tube and weld a short section of round tubing into place, through which I'd be able to remove/install the oil drain bolt.
2) Reinstall the engine cradle tubes I've cut out. Not quite as sketchy as it sounds, as I was really careful about how I cut everything apart and will be gussetting the swingarm junction anyway. No real advantage to doing this though either. Cutting off the old engine mounts and cleaning-up the tubes would take more time than bending and notching new tubing.
3) Buy a new frame. Seriously considering this option. Mostly because I'd kind of like to cut apart one of these frames anyway. Want to modify it to carry oil in the downtube, and maybe even fuel in the twin-spar part of the frame. If I go this route, I'd need to cut out the tubular hoop over the engine. Think that would give me just enough room to squeeze the engine in there. Going to watch ebay and see if anything pops-up.