Now that all of the work on the valves and valve seats is done I wanted to summarize the experience. My goal was to get the largest economical improvement. I'm a starving student, my budget is minimal. The porting modifications cost me a couple of burs and a ton of research time and e-mails to respected experts. Personal labour is free after all.
I don't see a reason why you wouldn't want to have the seats cut to three angle and the valves back cut, even on a standard rebuild. The cost was minimal, the turnover was incredible, I picked up the parts from the shop the next day. I mean just look at the two images below. The top is a standard valve and seat the bottom has the two simple modifications. Using Solidworks to simulate the valve comparison I found a back cut valve flowed 11% better than a standard one. These values are supported in articles by know experts such as D. Vizard.
I guess this post is a bit of rambling but I really think it's important to show those two images of Spitfire specific head and port. I will probably add to my porting guides page the collective information which I found useful from all different sources.
