His proform main body is a 67100c that is for a 750 aka 1-11/16
My proform main body is a 67107c. altho it is a lot smaller main body then the demon one. it tapers out to the 1-3/4 blade size or bore. Is designed for a 1-3/4 blade that is a 850 to 1050 cfm carb.
If you went up to a 1-3/4 throttle blade base on a 750 main body the blade would hit the main body
Go to post 78 to see the difference between a Mighty Demon 850 main body and a Proform 850 main body.