I've got some a stock 305 i am going to port and polish my heads in the near future. i am buying new valves, and wondered if i'm supposed to replace the old valve guides when you get new valves?.

 

It's a good idea... you can either replace the whole guides with bronze ones, or get the thin bronze bushings pressed into the existing ones. Either way, they'll last a whole lot longer than the stock cast-iron ones. Make sure that you get the top of them machined to .500" or .530" outer diameter so you can use the Teflon seals, which you can get from Crane or Comp. .530" is more common.