If its a RA celica, especially the coupe, it could be 6.7" solid rear axle (I think the early IRS RA Celica is also 6.7). So any R&P from a Celica Supra won't fit. Luckily you can get most ratios for the 6.7 brand new:
7.5" is tough, Nitro makes 4.10 and shorter, but finding anything taller than that is very difficult especially 3.73s - Although I did find a couple places in Australia that sell them new for around AUD$400 as they are a common gearset in the front of diesel Hilux trucks. 6.7" is actually easier as all the AE86 guys use that size, same with the older Celicas. 6.7" was a pretty common gear size for cars whereas the 7.5" is a lot more common in trucks so mostly only the short ratios are available.
I mean the real solution is to go to an 8" diff as the support is MUCH better for that size, which is what I am working on this winter!