No it has a better flow from the get-go, will increase compression and gets even better when you add the oversized valves, and a cam to go with it. Throw in a double roller timming chain and you now have a motor that is stronger than the original.
 You happy now WM.

Ditto!  Instead of your engine only making useful power up to about 5,000 rpm, you will now make useful power up to about 6,000 rpm, or even higher if you do more modifications.  I have an 81 22r block with a 76 celica 20r head, stock valvetrain and all, 4 into 1 header and weber 32/36 carb and it will gladly rev to about 6,000 rpm, whereas before it would stop making power at lK less.  The head design on the 20r is better.  You will not see a gain in the lower rpm, but will up higher.  Next time I will be using the biggest valves I can finagle in there, a mikuni cam, NWOR header, and possibly a holley 4bbl intake with a 390 carb, or fuel injection if I ever get around to making an adapter.