Yup, the Intro mid/bass drivers look similar but are actually quite different and definitely not suitable for the SBLs. Beware of of people selling “Naim bass drivers” on the usual online sites - I’ve seen a few that were Intro drivers!
Credos use the same type of mid/bass driver as SBLs, just not so tightly selected or matched, so they could be used in a pinch. Same for Allaes, but would be a shame to scavenge from them…