aye, you'd struggle for bulkhead clearance with that I think, although I dont know if harrop gives more clearance
could probably be done 🙂 but dont know if you need it 😛
60mm = 2822mm2
70MM = 3847mm2
80mm = 5024mm2
so 80mm is close to 45% bigger than 60mm
but then i guess you got more than 45% more power too 😃