360 exhaust mounting on gearbox

i think you miss a part there. there should be a square like bracket that bolts to the gearbox's back. I don't see it in your pic
the OEM exhaust is then bolted to the bracket, not the gearbox.

yes, this bracket should be on the rear upper part of the gearbox. there are 2 bolts and 1 nut securing it to the 360. same goes to the 430, although the bracket itself is somewhat modified.

 

Looks like you're missing something.