So I dug through Western Hills Honda's parts fische, 1980 cb650 & 1980 DOHC cb750's spoked wheels share:
front brake caliper
front hub & bearings
front axle
rear hub & bearings
rear axle
rear brake panel
The cb650 std and custom share the same fork lowers, brake disc & caliper, front axle. the only things that dont cross referance between the std & custom are rear sprocket carrier, rear axle.
So I should be able to use a dohc750 front wheel with my cb650c's brakes and axle, 750's rear wheel and brakes but I'm not sure on the sprocket carrier and rear axle and possibly spacers.