Can someone provide me with a list? I know the SA has no EGR (I believe, under the 2 primary ports), and the FB iirc has the mushroom on the front cover?

 

Only the 1980 12a engine has an EGR if I recall correctly, there are some minor differences (mostly with emmissions equipment). Also the later 12a's have a separate charcoal canister while the early ones have it built into the air cleaner lid.

 

What about literal engine differences? Like the SA having the eyebrows above the plugs, etc.

 

my fb has the half moons above the plugs

 

as far as I know the S1 engine had no gaurd on the plug holes, as the plugs are shorter (they dont fit a S2 engine I can say that for sure), the housings have three sort of dash mark equadistant around each hole, if the engine came in car form california it will most likely have the EGR ports (mine did) these engines have a solid cube ontop of the housings opposed to the I casting ontop. That is as much as I can come up with off hand, dont quote me on it but Im pretty certain its mostly correct.