The CRs that FunJimmy fitted to his CafeInterceptor 550 he modified the intake manifold so the rubbers and manifold brought them forward. The CB750 has the manifold fastened directly to the head, not bolted on like the 550. So, any way to fit shorter rubber intakes to bring the rack of CRs forward to avoid the interference? Or, is the distance needed too great?
Is your white tank designed for the cb750 motor or another motor?
Sounds like your only choice is to relocate the petcock location if you are going to fit the white tank, unless you are intending to raise the tank on the bike front and back to give the needed clearance for a petcock that hugs the tank tightly, pingle design maybe?