You could just use the stock valve, just cut the 45deg seat angle wider (2mm- 2.5mm) on the exhaust valve and 1- 1.5mm on the intake, this will increase the contact with the seat and will be able to disapate the heat better. There really isnt much difference with a "turbo valve" other than that they need to hold up with the extra heat, some are even sodium filled. Also the m42 motors had a 7mm stem and the m44 had a 6mm valve stem. So if your not gonna rev real high (above 7000rpm) then use a 7mm valve and will also cope with the heat better. Also taking about the busa springs they will only be rated at 15k rpm if valve train is as light as the bikes valve train and that is hard to believe. Also you would need solid lifters if your going over ~7500. With a turbo motor you do not need to spin it high to get the power so dont
, it will cost more and will break easier. I say run a stock valve with a wide 45 seat angle and shim the spings to 1.5mm to coil bind, if you want upgrade to a mm valve spring and shim that. This will also increase the spring rate and make a lighter valve spring more effective. Also RaceTEP.com sell ARP studs for the motor that you cant seem to get else where other than a custom ARP order. You will need these if your gonna run 20psi. They will hold up better than any bolt. Use a cometics MLS (multi layer steel) head gasket too as this will keep things in check with the extra heat and boost. Again TEP has them and I ordered a custom 87mm bore for the motor I am building.Please feel free to PM me with motor build questions. I used to build indy and nascar motors so I have seen how to do it if cost is no issue
. Also I started a motor build thread as I am building an NA motor for my friend. So if you want someone to build it let me know