The large pully/clutch in the front wont turn by hand, it wont even budge, it has over 2500 hours on it. Would it be safe to say its blown up?

 

not blown up just seized needs an overhaul more then likely

 

I have located two Mule 1000 vehicles. They both start and run well, but they both have over 3500 hours on them. Should I be afraid to buy them with this many hours of use?

 

mule 1000's didn't come with hour meters on them. It is probably miles and sure you will have to do some chasis maintenance, but that's not too bad if you can do it youself. If the motors were properly maintained, they are great engines. I have seen those models with anywhere from 5k to 10k miles on them.

As far as the mule with the engine locked, the drive side busing is seized onto the crankshaft. It can be repaired even without buying a crankshaft most of the time. The bushing has to be cut off the crankshaft with care then polished and new bushing pressed into the crankcase. Wha la going again.
Jody