https://www.model-engineer.co.uk/forums/postings.asp?th=136610
What an active forum on this interesting subject.... on pre war bikes I have always preferred cast iron. We still have some original valve guides for ohv's in our Sunbeam spares stock.
I don't like some of the suggestions in that link at all; Like you I prefer cast iron guides in nearly all my engines; it lasts a long time, much longer than bronze, its self lubricating and even for a lousy lathe man like myself, the right stuff is a delight to machine.
For my model one I was easily able to modify guides from god knows what to suit my engine.