Hi Ghostrider,
I hadn't seen the solid rear cab mount until recently either. If you hve the "1947-1954 Truck Factory Assembly Manual" reprint, you can see the solid rear mounts in an illustration on page 44 (counting the cover page as #1). The illustration is called R.P.O. 314 Automatic Transmission Instruction Index, Sect. 0, Sheet 13.00 .
I found that weird too and it is definitely on a 1/2 ton frame.
52 Chebby
