My 83 gts had a 6.7 (ra6x) my bros 85 gt had a 6.7 as well.. i Know he got a mki supra 7.5 rear end for his.. I got a mkii rear subframe with diff to upgrade mine to a 7.5"

the supra was a package of the celica back then.. so celicas might have 7.5 as well

If you can read the vin plate, here is a list of the codes to tell what gear it had.. its usually the last 4 on the id plate (not vin) http://www.celica-gts.com/resources/...ial_codes.html