I've got a 12a right now with the RB SP exhaust system....The whole thing. Do you think if I just bought the header, it would bolt up into an 84 -SE with no problems? Or is the header longer/shorter, and the exhaust mounts different?

I couldn't find anything searching.

 

iirc the only difference is the difference in port distance in relation to the header. Obviously the 13B header is going to be bigger because of the extra 10mm per housing.

 

Agreed - it's not going to be a 'bolt-on' fit, but an old rotary racer's trick is to plasma cut down the middle of the 'RB' symbol on the engine to header flange and then pull the pipes far enough apart to mount on the 13b. It's ghetto, but it works.

If anyone asks, I didn't recommend this - you should get the right header for the job,

 

I think what he means is if a RB 13b header will bolt up to his 12a RB exhaust and fit on his GSLSE. I don't know but you will definetly not have the 5th & 6th port tube.

 

The easiest solution would be to call RB or Mazdatrix and ask.

 

It will bolt up if you get the GSL-SE header.