okie dokie, i've got a header for a gen 3 3sge (as the title suggests). it came off an ST202 celica (i.e. import to oz, 3rd gen 3sge), i think its the same engine as in the mr2's. BUT i think it'll only fit on a fwd as it is - its 4-2-1 down to the cat, JASMA approved, and full stainless steel (v.nice )
i've had a few ppl suggest that it might fit on a 3sfe engine too - celica and camry, but i've got pics and all the dimensions at the link, so get it measured up first so you don't have the same problem i did!!!