[TRX2fiveO]

Clean your head up with Emory cloth and polish. If you put the bearings on the cam and place it in the head you will see that the cam does not touch the head. Under heavy torque it may flex a little but if you clean that up you'll be ok. I've done it before with no issues.
Use a UNI filter too Much better for off road than a K&N
Also replace the timing chain with Part# 14401-MEB-671 this is a 02-08 CRF450R/X, Replace the guides too and tensioner.

 

[TRX2fiveO]

If you're going to replace the intake valves it's best to just go ahead and replace the exhaust valves as well I used all oem valves and Kibblewhit springs ..I have a stage 2 Magnum cam will the stock valve guides .. as far as the Piston goes wiseco is a good piston JE is a good piston but if I've said it once I've said it a thousand times your engine is only as good as the Builder I had a JE in my 250 x with the 80mm Big Bore Kit and I'm running up 11:1 88mm Wiseco in my 400. I also run a manual cam tensioner and a CRF450R chain make sure you replace the guides to the timing chain part number is a 14401-MEB-671

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[TRX2fiveO]

Yes you should be able to buy just the gasket. . . Make sure it's the MLS type (multi-Layered Steel) Wiseco sells them too