Quinn G - your profile shows you having a Model 100. If that's the tractor you're working on, and it has a 10hp Kohler K241 engine then you can see on Kraig's post the torque should be 25-30 ft.lbs.
I'm not sure where you're seeing 200 in.lbs. in the manual you have but 200 in.lbs. converts to 16.66 ft. lbs. which only applies to the 8hp K181 engine.
Additionally, when torqueing your head bolts/screws make sure you follow the sequence shown in Kraig's second chart pic. Assuming your engine is the 10hp I'd suggest starting at about 15 ft.lbs. for each bolt/screw, then start the sequence again and use 20 ft. lbs. and then the 3rd and final time use 28 ft. lbs. as your final torque.
Ed C - real shame one of your drive shaft couplings really tore up your hydrostatic pump input shaft.
It's hard to say what your first steps should be. You can attempt to fix yours but no guarantee it will hold together because of the amount of shearing on the pump input shaft.
Looks to me like you need at least a new coupler and spirol pin (as well as the new filter and also fix your wiring). I suppose it's worth a try but it could just blow apart again.
Finding a parts tractor may be more ideal. I've never seen this problem before so assume it's not common and most likely the hydro pump input shaft and the coupler on a parts tractor would be in good condition, and you'd end up with some additional spare parts. However, the hydro pump trunion on the parts tractor will likely need the usual fixing up or you'll end up solving your current problem but the tractor will slow up hills, speed up down hill, or lurch/jump.
So, what's a guy to do??? Maybe see what others suggest on here while you search for your needed parts or a parts unit. Instead of a parts tractor you might be able to find a used hydrostatic pump that has the trunion already fixed, a used correct coupler (hard to figure out from the parts list), new pump gasket, new filter and new spirol pin.
You need to study up the info in your Service Manual and determine if your tractor used the coupler that also had a ball bearing for centering. That may have only been used on some of the earlier 1x9 wide frames. I don't recall if it was used on the early 1650 Quiet Line tractors.