Long gap here but the past few days during lunch I have made some progress on this project!
I cut up some of the 2x3 (.120 wall) tubing for the frame rails, and some 2x2 (.120 wall) tubing for the rear drive motor support, battery box support, and front pto motor support. I thought my work had some 2" OD tubing kicking around I could use for the Bolens front end attachment, but it's 2" ID so no go. I ordered up a 3ft short piece from eBay. After that arrives it's a matter of welding up the new frame structure. I'm thinking I will go period correct on the welds and stick it together... Maybe cheat a bit and use the mig for tacks.
In the meantime I finished dis-assembly of the tractor to the point I need it to be... I removed the front grill, steering, rear fenders, lift mechanism, and cut the original frame tubes off near flush with the rear end.
The new 2x3 tubes will rest on top of the rear end. I'm thinking I will weld a piece of angle iron on the inside similar to the fender mounts and bolt through the 2 brackets, tube, and fenders to attach the rear end to the frame rails. I'm also leaving about 1.5" overhang off the back of the tractor for a future rear 3pt hitch setup.
Sorry for the lack of pictures. When I get to welding and mockup on the rear end and new front assembly I will be sure to snap some pictures!