Originally Posted by Pr1ce
Bronze /= brass. Never use brass for guides, bushings, any type of wear item. It machines well because it's relatively hard- comes off in a sand-like spray, gets everywhere and in everything, including under the carriage of the lathe, way covers of the mill etc. Makes a mess. You'll have little brass pile in the shower when you wash your hair after a long shift turning the stuff on a conventional lathe w/o guards.
I don't believe the brand should matter, bronze guides made for that intention should have been spec'd correctly to begin with. They are not a high-wear item; seals are, but you'd be pressed to put extremely high miles on an engine to wear the guides, particularly with synthetic oil. Some engine building companies brand their bronze, such as Bronzanium 90, manganese-bronze, Ampco something or other. This is all assuming an aluminium head- CI heads can use ignorant cast Fe or better yet, Dura-bar (awesome videos showing how Dura-bar is manufactured are available on Youtube- yes, it's "cast iron" but continuously cast as round bar). Dura-bar is great for brake rotors, valve guides, bearing blocks...machines like a champ too.
NB: not any ol' bronze will do. Clearance between a valve and guide is on the order of 0.0005". It is a requirement that the bronze be a specific alloy or narrow subset thereof to be suitable for use in an automotive valve guide. The operating conditions present variable heat distributions and high-speed cycling of relatively short rectilinear motion by hardened and highly alloyed valve stems, hopefully with an oil film. Go with a known quantity.