Mower Tear down but hit a wall

Hey Guys, I'm new to this rebuild world and started with my dad's old '89 JD Hydro175, with kawasaki 15hp. I got the engine running again, after sitting some years, and starting tearing down. I pulled off everything non-essential, next step was to swap drive pulleys out. Then I found out Hydro's just can't handle the swap so trying to figure out am I effectively dead in the water?

I figure I could pull off the back axle/transmission from another tractor and put onto my frame or I could just start over with a different tractor all together. Not sure which would be more constructive at this point.

What would be some positives to look for in terms of chassis and transmission in some other Lawn tractors?
If I found an intact mower with bad motor would it be easier to switch my motor over vs transmission swap?

@Maine Mud Mower did a build a few years back with a hydro, and if memory serves right he moved the hydro forward and added a set of chains running back to a live axle (if you want the diff look around for a peerless 100) and thus the hydro is overdriving the axle. He has a YouTube series about it, search “hydro mudder”

Just throw a gear drive under it