The front or rear mounted engine bit is not what gives the opposite throw. Either way it will throw to the right if 'directly' driven.
The left throw machines have a front mounted engine and the cutter belt runs aft, does a 180 degree turn behind the deck (this is the tensioner) and then on to the deck. I'm talking tractor models. Without the 180 degree turn they would also shoot right
Your stallion, rear engine of course, but the cutter belt must also run direct to deck without doing a 180 (?) and so had a different clutch/tensioner arrangement - and opposite throw
The HD8's had a horizontal shaft engine with the PTO pointing forward and a 'direct' line to the deck. The belts ran under the engine
Many ways to skin a cat
