Honda used to reccomend plain ole 10W30 in their shop manuals. My '92 Helms manual says to do just that. Then around '96 or '97 they started selling Honda MTF and voila, the newer manuals magically all say to use Honda MTF.

You can also use Red Line MTL. Not sure about Royal Purple or if they have a compatible oil. Basically if you find anything that's roughly equivalent to 10W30 it should be fine.