webcams is another cam maker. Alot of people have had luck modifying the trx450r exhaust pipe to fit the stock 350x head pipe. Not sure how costs are running on the trx450r headpipes nowadays. Not sure how crazy you are wanting to get with your 350x. Of course poweroll will stroke your crank and you can get their big bore stuff. Stiffer springs and hardened rockers are a must as well. Get your frame reinforced or it will crack if it hasn't already. And there's a ton of small mods you can do as well, though not all are for power, some are for other things, like brake lights. Best of luck and have fun.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90