I'd recommend SI Valves if you're looking for bronze valve guides. They are a reputable company and make ones that fit the 4ag valve guide bores properly, have the proper oil clearance to start with, and also fit standard valve stem seals properly. They are maganeze bronze, as are many of the better ones now available. They can be found here:
SI VALVES
I have some being installed in a 4agze I am rebuilding. I'm having the machine shop put mine in, as I didn't want to take the chance that I might damage them, plus they may need to be slightly reamed for the proper oil clearances.
For valves, however, Supertech definitely make some nice ones. I got their undercut standard size valves, which are ss, nitride coated, and back cut. I'm having a 5-angle cut done on them. Whether or not that will be significantly any better than a 3-angle job, I don't know, but you only live once.
