Welcome!
The tires were your biggest down fall, start out in 2nd, but you better make sure you do some dry runs to make sure your not going to bog it out the hole. As for the jetting, pretty simple if you think you can take the carbs off enough to get the bowls off and get the mains out. That would be the one right in the center with like a plastic cup deal around it. You could replace with 240-260 if your going to run with no lid, if not just leave it. The other jets will be fine, but unless you have a proflo adaptor or something simular the filter will not stay in without a lid. Now when you get pipes thats whats going to wake it up and if you keep the lid on 280 main will do, and lid off 290-310. Hope this helps, you may be able to find a clymers manual download.
Just to let you know, the 450s are pretty sick, so dont feel bad if you get beat with your mods. Good luck!