I did some searching, but couldn't find anything to nail this down totally. Are the pedal clusters for all S30s interchangeable? Can I use one from a '77, for example? Or do I need to find one from an early car to go in my early '71?

Arne,

Generally speaking, I have found that the parts of the later S30s are quite different from the parts of the earlier S30s. Not to say they won't work, but I just seem to find there are subtle differences that make swapping things out one-for-one difficult. Pedal cluster 48318-E4601 goes through several part # changes begining what looks like in 7/72. There is a different # for the 2+2 and automatic. Looks to me like you have N3300 for the cars around '72 - '75 and N4700 starting 8/76.