If your looking for performance than port and polish if you are wanting to refresh or replace valves then get a valve job done. I will try to exsplain port and polish as i have had a few exsplain it to me today. A valve job and a port and polish are not the same. A valve job a standerd one is wher they cut and reshape your valve seats/ports by doing a 3 angle port job. You may want this or need this when replaceing valves. I found the stand 3 angle valve job price from 100-175. A port and polish is wher they can go in and port/polish the port and head and can bore out the ports for larger valves but you can port and polish without bigger valves. port and polish is costly 350+ but you gain some good power. Personally I would get everythang else done before port/polish like your full exhust, jet kit, bore high compression piston , cam , new/better rod /crankshaft and all the thangs like better clutch and 1way so it hold up before I pay for a port and polish. Atlest for me anyways a port and polish and fcr carb are the last performance mods i have on my wish list "turbo/nitro/rocket be nice but is unrealistic for me to do"