I've got disc brakes and adapters ordered, also for the front with an adapter.
I laid out the drops with vice grips after bending the chain stays for the wide rim. I bent them halfway back to make room for the cranks, it's a standard width BB.
It lines up nicely with the stays and the twin bars that will transverse the bike. I had thought of bending the twin bars to fit the 4" tire, but it will clear the tire without bending. That should be better for strength as they will be the seat stays. I just have to brace it at the seat post where there will be a 3"+ gap. Maybe a plate welded in. The twin bars also look like the ends will slide in the existing tubing on the drops, so welding them up should look pretty clean. I may just bolt up the bottom halves instead of welding to get a little adjustment if need be.
Finally for today I checked the fitting of the wheel and it looked good. I finished up at 1100 am, it's too hot already. And I couldn't do any cutting or grinding with clothes hanging up drying in the shop.