This is very similiar to the saw set-up that my Dad had for the 1955 cub that I now have, except the saw was mounted on the fast hitch carry all. This allowed for easy relocating from one pole pile to the next. Wish I could find some pictures to share with everyone.
There was one drawback to running the saw with the flat belt and the larger flat pulley on the PTO as I am sure Brent has also noticed if he has used this set-up much at all. The larger pulley on the PTO (9" I believe) turning the smaller pulley on the saw mandrell made it neccessary to run the tractor engine RPMs at a considerable slower rate then would have been desirable. This was neccessary to keep from overspeeding the 30" saw blade.
The end result:------ After extended use, and lugging the engine to very low RPMs, which also resulted in very low oil pressures as large pieces of hickory, oak, elm, etc. were feed into the saw, the hammering action of the pistons/rods as they continued to work at keeping the crankshaft turning, coupled with the low oil pressures literally destroyed the upper half of the rob bearings.
Brent, if you are reading, I firmly believe this set-up would be much more efficent if you could locate the small pulley (6" I believe) for the PTO, or possibly run through a dual belt set-up using a jackshaft with different size pulleys at the saw frame. Looks as though you may have a jackshaft on the saw now. This would allow the cub engine RPMs to run up higher and closer to the power curve, while still maintaining a safe saw blade speed.