Found it. Credit for calling local shops goes to…75ticksparkThanks, guys. I need to find the post, but it’s not my own idea. May even have been Nealric who made that wise suggestion when I started asking the question a couple months back. As always, I appreciate the input from the team here. Thank you.
I don’t have any objections to that advice. I wasn’t sure if it would be problematic having no crossmember of any sort in place.I'd be doing the cross member build last.
Get the engine and gearbox in, fully bolted up. Engine sump, brake master cylinders, etc all in their place and you very happy, I.e. no more unsolved questions.
Then finish the conversion by making the cross member and engine mount solution
Your statements track with my gut feeling. My plan was to tack in my frame plates (orange in sketch below) on both the driver and passenger sides, then tack a tube steel crossmember (blue) to the plates that bolt to the frame plates. This will lock the present geometry into a reference crossmember before I cut out the tube I had tacked in (red squiggled out in picture below) prior to cutting out the original crossmember.About structure: When you cut major structure (like a roof, or crossmember) you must make provisions to get everything lined back up correctly when you restore the structure (like roof or crossmember). So hopefully, you braced the bodywork before the cut. However, I remember the Alfa Spider as having huge amounts of cowl shake (read this as, if you didn't probably wont matter that much).
Anyways, I have cut roofs and realigned, it's amazing how much flexing occurs without a roof. My Milano is noticeably less torsionally stiff than a modern BMW (this may be unfair comparison due to vintage, but E30's are also stiffer). If I jack up the right side, it takes a bit before the left side comes up, this happens quicker on BMW's. Anyways, for a convertible, torsionally weak from the beginning, I would still have tried to brace that interior space to minimize the body twisting.
That bar you have for the purpose of restoring geometry seems to still be in the way for fitting purposes, especially as the sump is where that bar is.