This is what you might want and could use, and IMO with a few alignment/witness marks sharpied-on before going in might help make the fender saleable if not usable. With a tad of practice/skill one can easily remove spot welds without drilling through both components. Grind the remainder of whichever side flush and puddle-weld once in position, either from pics
shown or tacked while in situ, perhaps your way to a decent fit.
Amazing deals on this 3/8In Double Sided Rotary Spot Weld Cutter at Harbor Freight. Quality tools & low prices.
www.harborfreight.com
btw, IMO w/o the engine cradle (AKA sub-frame) to also check/align to any front clip fit can be a guess. 'Loose-assemble' as many things you can 'qualify' (AKA 'locate') to help get the other bits in line.
I have a spot weld cutter like you suggested. I used it a few times over the years, and if used carefully, works pretty well. Yes, if using the removed piece again, you have to grind the remaining spot weld flush to get a good fit. I usually give it a coat of weld-through primer before plug welding the parts back together.
The fact is though, that it would be a large amount of work to completely disassemble the fender and supporting pieces and then weld it all back together again. Especially problematic is the rear edge next to the door where the skin is wrapped around the internal support, crimped, then welded again. Even then, the curve at the front next to the hood is wrong and would have to be cut apart and reshaped. I just don't feel like tackling that much work is worth my time and effort.
The subframe is bolted up in the proper position with new mounts, and was located using the alignment holes and 5/8" pins in the forward subframe mounts and the body mounts as spelled out in the assembly manual. Misalignment of the subframe will have more of an effect on the proper wheel alignment with respect to the rear axle than with the alignment of the fenders, because of the large holes at the front where radiator support sits on the subframe. The holes are ~1" and the bolts are 1/2", so there is plenty of tolerance at that point. The radiator support is new also, and when I compared it with the old one, other than it not being bent near the left headlight mount, it is nearly identical. It sets just where it should for the fenders to attach at the front.
At this point, I decided to order a pair of new fenders from a dealer that guarantees their fenders will fit and are very good quality, for only $50 more a piece than regular stock fenders. They expect them to be in stock in mid-November, so I'll have some time to work on other parts of the project like the seats and a few other items.
Near the top of the list is to drag out the engine I built up to put in it and get it fired up for the first time. It's a 434 cu.in. SBC stroker motor, built on a four bolt 400 cu.in. Chevy truck block. I'm going to mate it with a TKO600 five speed with a .64 overdrive. That with the 3.55 rear gear will give me a 60mph cruise at about 1900 rpm.
The original numbers matching 350/300hp L48 engine and M21 Muncie transmission are overhauled and pickled for storage.
Thanks for your suggestions.