I buttoned up some more repairs today by finish welding the undersides of the welds I previously made. I finished under the core support mounting tabs, behind the crossmember mounting areas and under the cab mount supports.
Here's the front side of the crossmember repair after welding on the rear.
I decided to remove the cab mount supports from the frame rails since I found so much rust behind where the factory spring cups were. I want to make sure the rust is completely cleaned off and out of the crevices before painting or powdercoating the frame. There wasn't a whole lot of rust behind them, but enough that I feel good about removing them to clean it all out. It will make cleaning them easier because I can use the glass bead cabinet rather than trying to work around them on the complete frame rail assembly.
These welds look sloppy, but they will finish out ok once I grind them down.
I also found my transmission. It is a TR3650 from a 2004 Mustang. I got a nice clutch, clutch fork, pressure plate and an aluminum Cobra Flywheel for next to nothing because the transmission grinds between 1-2. There was a recall on these transmission built from 2000-2002 where Ford changed the synchronizer assembly for 1-2 but by 2004, it should already have the good parts installed from the factory. My theory is that either the transmission is a 2000-2002 model and the seller didn't know (or didn't tell me), or that the previous owner just didn't have the clutch adjusted properly. Either way, it may need anything from a set of synchros to a full overhaul with a couple new gears. If it needs a full overhaul, I'll probably find a replacement for it.