Nutcase,
I am no expert in the world of GT pulling, though I would consider my self very knowledgeable about truck and vintage tractor pulling as started when I was 13. People keep referring to Brian Millers site like he's the god of GT pulls (not saying you did but others have). I have looked at his site before and was not to impressed. I can also tell you hydrostatics, if properly set up, can dominate in the pulls. Where I pull there is a John Deere 318 hydro that pulls in the 20hp class and just destroys the competition. There is also a old Bolens ( don't know the model) that typically finishes in the top 5. Now while I'm not trying to claim these are bone stock machines they are not all out modded pullers either. Like I said before most GT pulls have very vague rules. Our rules say the motors have to be stock but say nothing about the rest of the drivetrain with the exception of welded diffs, that's a no no. So the cub guys run different pinions and billet clutches in their tractors. The case tractors are hydraulic drive, not hydrostatic (as I am sure you know) and I believe they can be made into a great pulling tractor with the time and money. I really believe one of the main problems with trying to use a Case as a puller is their gear ratio. Before I stopped pulling mine last season my biggest problem was the engine stalling. It felt as if though I was trying to pull the sled with a cub in 4th gear. I really wanted to try a 400 series motor but money got a little tight for projects and I never got around to it. I will have to admit though, the best bang for the buck would be found in a old cub cadet, but at the same time whats the fun in doing something everyone else does?
ByCo, I know nothing about the 210s but it sounds like they would defiantly be worth a shot. As for me I am building a cub 124 but am going to continue to experiment with my 224