Is the wheel offset to the right mate? The front wheel needs to be exactly central to the forks. If your wheels aren't in line, (in this case, possibly offset) the bike won't track straight, it'll "crab walk" down the road requiring constant corrections, wearing your tyres unevenly and will handle like sh1t.
The problem with trying to mix and match modern parts with old bikes is that unless you do it properly (the most expensive route, usually) you can end up with a bike that is gonna try to kill you every time you ride it. Modern bikes forks are usually shorter in length, so by installing them you're effectively dropping the front end down, which will "quicken" the steering, making direction changes faster, but losing straight line stability.
To exacerbate the problem, if you use the CBR's stock triples with steeper geometry than a CB750, you'll further quicken the steering to a dangerous level. So with all of the above, you may have a bike that won't track straight without constant corrections from you, will try to fall over going into corners, will wear tyres unevenly, and will try to throw you down the road. Not ideal. Cheers, Terry.
