I can think of a couple of things right off the bat that I did to my 1250.
You will probably need to replace with OEM rubbers the Engine Isolator mounts. The originals wear out pretty bad and cause alignment issues with the drive shaft.
Second, in order to keep your new ones from wearing out, you should do the cradle mod. This is a piece of 1inch flat stock welded to each side of the engine mount at the front just forward of the oil pan.
Third, replace the drive shaft and get all new flex discs front and rear. I doubled up the discs in the rear and used one in the front. There is also a bushing in the front flex disc mount that the drive shaft slides into for alignment. Replace this also.
The last thing I can think of since you will be that far into it, is to check out the trunion on the transmission. If it is wore you will need to weld up the corners and wear spots and make it true again. Replace the two trunion springs and guide pins.
These are the main issues I can think of with the Quiet Line series Cubs. Your's may not need all of this, but these are the things I would look at.
Oh, the trunion is what makes your hydro work smoothly. If it wants to jerk or takes off suddenly, then it is wore.
We are happy to help out anyway we can. There is lots of information on the items I posted above here and from the other great members here.
This is the cradle mod I was talking about. The horizontal piece has to be welded in:
This is the cradle mounted to the frame, also the four corners with bolts are the ISO mounts I was talking about. One half goes on top and one half goes on the bottom. Don't buy the cheap imitations.
These are the bushings I mentioned. One in the front and one in the rear:
This was my 1250. A great tractor, you will like yours a lot:
