Do you have a cab? For some with a rear mount snowblower or possible using a back blade in reverse a rear exhaust is bad as your are always backing into the fumes. I put a vertical exhaust on our similar tractor this year but it has a cab and I just mounted a piece of exhaust pipe to it and welded some flex pipe and a few pieces of exhaust pipe to it and joined it to the original muffler at the front of the tractor.
Al