Can you not use the old ones to know the size? I will guess with all the models Bush Hog has made there could be more than one size used and also where on the cutter they are. They also have rough cut and finish mowers.
I have a Bush Hog rear finishing mower and think the fittings on the wheels are std 1/8 pipe threads (think have the 1/8) right. Think those on my spindles are same but I want to move to longer ones to make greasing easier. No idea on the pto shaft.