Are the VT750 and VT600 Front Ends Compatible?

Are the VT750 and VT600 front ends compatible?

NOPE!

These bikes have very different front ends (e.g. steering stem length, steering bearings, etc.) And the size of the fork tubes is also different: the VT600 is 39mm; the VT750 is 41mm. I guess you could cut the neck off and use some specialized machining to make it happen but it's not a simple process.