I'm sure this has been asked before, but the search isn't working right now. I have a 98 ls1 with stock perimeter bolt heads. I want to have them ported/polished this winter, because I don't have the money to buy new ls6 casting heads. Can I run a bigger size valve in the stock head? Is it worth the money saved? I also plan on bigger valve springs to handle a mild cam. My friend works at a machine shop and isn't going to charge me for the work, I just have to buy the parts. What do you guys think/recommend?

 

Yes u can.

The valve seats are 2.02 in diameter (int) so it is actually pointless to run bigger than that on stock seats. As a matter of fact you might see a 5 cfm difference between stock 2.00 and 2.02 valves.
IMO, don't let anyone that is not a LSx head porter touch your heads. You might be sorry for the results. Save some $$$ and get TSP or PP stage 1's instead.
Otherwise, PP will give a good deal on ported "perimeter" castings, <$1000 with dual springs.