Re: First build, Electra Cruiser
I think your new mount will be fine. Thickwall tubular spacers used like that are pretty strong and resistant to lateral forces. Very similar to the design and use of shoulder bolts used on some machine tools. Just re-tighten everything after the first run.
If it start showing signs of trouble, I would then go with Jokes good idea with the angle irons. You could clamp them together in place, then take the clamped assy to the bench and drill and bolt them