I know this isn't a C10 and off topic

[3drburb]

Thats a very nice truck you have.
I think you are on the right track with the frame, but keep in mind that the Divco have the steps into the van and the newer frame may be a little wider if so you will need to alter the floor but that may be needed to add seats anyway. If you find a 3/4 or 1 ton truck frame it should work better because the weight of the truck. You can also consider putting the newer crossmember and rearend on the old frame, this maybe be the best way to do it if the old frame is still solid.

I am considering this on my 1946 Chevy Package Delivery with the 127 wheelbase also.

Be extra carefull with this one its a very top heavy truck.