I looked at doing it way back when I had my RXL. If I remember correctly...which is highly unlikely...it seems to me the two engines were ported differently. I think there were some runability issues when you put carbs on the EFI engine. I never ended up doing it, so I don't know for sure.
I had bought a 92 500 EFI that my friend converted to 44 Milkunis . a twin vacuum fuel pump. twin PSI pipes, and air pods. it went over 20,000 miles on original motor. had a dead spot we couldnt fix. just lived with it. but he had a donor 500 he took everything from, thats the easy way. if you are looking for all individual parts. little harder. have had 2 more EFIs since then. a now another 500 EFI that starts in 1 pull everytime, so leave it alone till the time comes.
why not fix your RXL., great running sled when they work.