Sounds like it has had some engine mount modifications already , so a little more wont hurt!
Thankfully, the 39 GMC Frame was in such good shape. I guess sometime in the past though the 39 had swapped transmissions and it had a PTO shaft out the side that necessitated cutting a notch in the transmission cross support so I used the transmission crossmember from the 40 Chevy that was still in good shape.
