Hi, sorry it took so long to get back to you...
So as DJ says, use as much of the EX stuff as you can, there are very good pads available that'll make that disc work juuuuust fine for any speed you'll make with the 450. Dig up a CB360 disc and.....bolt the EX disc to theCB carrier just like he did. That should bolt to your 450 hub IIRC. The stem bearings should be the same for the 450 as on the 360, though be sure to verify. If not, just drop an email to allballs and they will likely set you up directly. The EX front end is a nice budget setup for what you're doing and the top clamp can be dressed up nicely. Get yourself over racetech, they can make you springs to suit whatever weight you need...just wait till the bike is mostly done before that step so you get the right weight. You can also get emulators to fit those4 forks that'll take them from good to very good on rough roads. The other good thing about that front end on a smaller bike...it's light compared to stuff from bigger bikes and weight savings are going to be a boon to performance. You'll be pleased with it once it's on and dialed in.
If you do decide to swap to a larger front disc (seriously, try the 250 disc with ebc or galfer pads and braided lines first) there are several almost bolt on options for your 450 hub and as PJ says, making a caliper bracket is easy as pie. If you can do basic maintenance, you CAN do this conversion.