oh yeah... that makes sense i guess..
six inch over, pipes... pipes 6 inches over stock... i think they usually call them tubes though.. pipes are exhaust... when i think of an over pipe, i think of this
http://www.suzukicycles.org/photos/USA/1969_cards/1969_T125_Stinger_850.jpg he's probably making a bobber.... most people just... lower the hell out of the back with some short shocks, and cut the frame to sit lower, chop the butt off of it, and make a little seat to sit on...
but with that said, don't look for 6" over cb750 forks. you'll never find them.. just... look for 6" over forks period, that happen to fit the diameter of the triple clamps.. They don't have to be specifically for the cb750....
harley tubes are probably too fat... but... if you're modding a bike like that, you gotta figure out how to make things that don't fit - fit to achieve your overall goals.. you'll have to use whatever disk brake system comes with those tubes...
unless you are good with fabrication
-Your servant is your master-