Rob,
I would start looking at these;
"A Toyota G-series diff which is an 8 inch unit (instead of the 124's 6 inch), fitted with the late model (90's) heavy housing 4.556 ratio 4 spider LSD. Works out to be 32mm wider than the stock 124 unit. This is only 10mm wider per side once you remove the Fiat steel wheel spacers. The complete unit including brackets is approx 18.9kg heavier than the 124 unit. A further 4.2kg can be saved by using the pre 90's LSD head which has a different casting."
I believe these are found on early pickups and forerunners.
The above is copied from this thread;
http://www.turbo124.com/forum/viewtopic ... oyota+diff
It is a reasonable long discussion of alternate diffs for 124 coupes. I do not have much useful to ad other than a couple friends have been in the Toyota truck scene and support is quite extensive.
The weight increase is unfortunate. Although in your case, i think you will have power to spare and weight may not be a deal breaker? Also, I feel the FIAT diff suffers (under abuse) from its light design and fabrication.
Cheers,
Jordan
