what valve seals after machining guides?

Have the guides cut to .630" outside diam(IF STOCK HEADS ARE USED), have them cut down about .100", this will give you plenty of room with the seal installed. Make sure the guides are not too loose, if they are just have them install some liners.

Dont use the stock type seals and definitely use seals on all 16 valves. I like to use seal like the one here in the pic. Its called a Metal Body Vition. They last a long time and work well.