I have 6 mm guides with a .447" OD made from the same material as the stock ones.
I also have bronze guides that have a .445" OD and are 1.250" long plus any other 305/342 parts you might want.
920-207-9180
Not that i know of.
I also have big valves and seats for the 342.
The exhaust valve has a slightly larger stem to compensate for the loose guide.
I do not have larger stems for the stock size valves.