Cyclo Benelux offered a 2 and 3 speed conversion for SA hubs and these came with a Mk 7 pull chain derailleur and a top tube shifter... other derailleurs could also handle the wider 1/8 chain and work better.
This kit was sold for many years and one can also do a dual drive conversion using 3/32 Shimano cogs which will fill the space that was occupied by the 1/8 SA cog and spacers.
My commuter runs an AG 3 speed with a dual drive... as the bike is not an old Raleigh but a more modern bike it was set up for 3/32 chain and is quite a nice set up as the 18/20 in the rear provides a nice half step gearing.