If you're serious about 12K rpm, then you need two things....deep pockets and get a thorough understanding of where HP, Torque, RPMs and the associated engineering for each come from......ie: the book "How to Hot Rod Small Block Chevy's". Ironically, much of hot rodding engines, even today, come from lessons learned in making WW2 fighter plane engines faster, better, more reliable. No engine has been more thoroughly modified than the small block.....good to learn from what worked there. If your engine is bone stock, then it makes max HP at 8500 RPM, even tho it red lines at 9300. Those extra 800 RPM just burn more gasoline and return nothing. To shoot for 12000....you're asking every in that engine/drive train to do 40% more work. That's a lot.
In a nutshell, I don't know what you've already done to your engine, but rest assured IMO, starting at the top end will begin a lengthy and expensive series of tear downs. Piston skirts shortened (and of the correct material!) lightened piston pins, rod modifications, crankshaft rebuilding to lighten and balance will do more to get your magic RPM's than shaving the warts off of a stock cam shaft. One thing you may want to pay particular attention to is the cam chain itself. I can't say I've ever seen any numbers that give it a known upper limit on its integral strength. Then there's the whole system of springs, rockers etc. that the cam touches. I'd be very leery of using a slipper foot rocker at those RPM's. Look at the amount of skuffs and 'chuck holes' in the stock engine rockers. Good luck and let us know how you make out.
