Look any of the CBR or other 600 sport bikes. The front suspension is much heavier and larger than your 400. Then there is the question about the front tire. Will you use the original or go with the one from the new front end? The original wheel will look silly on an upside down fork. If you use the new wheel, what about the rear wheel? The original rear wheel will look odd with the new front. If you use the new rear wheel then you need a different swing arm and the sprockets won't align. By the time you have the new forks, swing arm, wheels and mod to the engine case and sprockets, essentially you have a CBR600 with a 400 Twin engine.
35mm CB650 or CB750 dohc forks will be easy. You need one of the shorter (stem) triple trees though. CB650 triple is a direct swap,CBX and others might be the same. CB750 dohc triple would need either your stem pressed in or custom stem/spacers. All easy and achievable.
A forum community dedicated to Honda Twin cylinder motorcycle owners and enthusiasts. Come join the discussion about performance, engine builds, classifieds, modifications, troubleshooting, maintenance, and more!