Looking at the pictures there is quite a lot of difference around the valve. Another thing i was going to mention and what rob bought up was cams. Surley they will play a big fact on valve lift and duration for gas flow. Im running a power engineering stage 3 head and there own regrind cam sx428t. I have just bought my t3 stage 3 so will let you all know. It wont be for a few months tho lol