Here is the explanation on why they changed the mounts:
...the idea of the three-point system was to let the frame flex without affecting the cab. This worked well, but the single forward mount put too much stress on the front frame crossmember, so two smaller shackle mounts were set on the forward chassis rails instead. The cab was still unaffected by frame flexing thanks to the lessened tension of the shackle bolts...
I'm not following how changing the rear cab mount affected the front radiator support mount. When you say "two smaller shackle mounts were set on the forward chassis rails" what do you mean by forward rails?
I also don't understand "lessened tension of the shackle bolts"
I'm familiar with both kinds of cab mounts as I have a 48 and a 53.
Grigg