Would a RB 6-port manifold for the SE engine fit a S4/S5 6-port engine?

 

Don't believe so. Which intake are you looking at, the Holley style or the wrap around 2-barrel one? If you're looking for the the wrap around one, RB does/did make a UIM that mates up to the S4 LIM 6-port intake mani, I have 1 of those. If you're looking at the Holley style, I believe it needs some sort of an adapter flange. If you're dead set on the Holley style, look into the Jay-Tech manis, they flow better anyway and even make ones for the TII and FD engines. I just recently sold the one I had for an FD. While the Jay-Techs are more expensive, they are better units

 

I am looking at the one for the Weber 48 IDA

 

Yes it will fit. The only difference is the primary port runner size. The SE primaries are smaller so you'd have to grind a little bit to make them larger to match. Everything else is the same.