This is what Wikipedia has to say about the W58 so im guessing anything above an 86 had the same length extention housing as the MKIII? even it it did though wouldnt there be differences? How would i know if it would be compatible with the MKII w58 or if it would even fit right into my MKIII?
"It differs from the W57 in its fifth-gear ratio. This transmission is popular as a replacement for weak stock transmissions in other vehicles. It came in two varieties: the original found in the 1982-1989 non-turbo Supras, Celicas and Cressidas of the early 1980s; and the later version found in Mk3, Mk 4 Supras and Lexus SC 300s.
Toyota lists a change from an alloy sandwich plate to a steel sandwich plate around 1989. The steel sandwich plate has some minor internal differences, and it is believed to be slightly stronger (some wider bearings, some wider gears, slightly different gear selection mechanism, etc.). In theory the all-alloy version of the W58 should be exactly the same strength as any other all-alloy W-Series transmission. The steel plate version is considered much harder to find and worth approximately three to five times as much as an all alloy version.
The ratios and bolt patterns remain the same regardless of the sandwich plate used.
The W58 & W57 share the highest gearing and closest ratios (1st, 2nd, 3rd, and 4th (direct)) of the stock W-Series transmissions.
The ratio shift was accomplished by taking the W55 base ratios and changing the input shaft to intermediate shaft ratio by 7.9%, thus shifting 1, 2, 3 ratios higher by that amount. This also shifted the overdrive 5th gear higher by the same amount creating a wider and taller overdrive ratio.
The W58 is sometimes designated as a "close-ratio transmission"; however, in its stock form it does not meet all the criteria for a close-ratio box.
Toyota engineers have shown favor to the W58 over the rest of the 'W' series by including it in so many models and even building a stronger version for higher powered applications.
Ratios:
First Gear: 3.285:1
Second Gear: 1.894:1
Third Gear: 1.275:1
Fourth Gear: 1.00:1
Fifth Gear: 0.783:1
Reverse: -3.768:1
Applications:
1982-1986 Toyota MK 2 Celica Supra
1986-1992 Toyota MK 3 non-turbo Supra
1993-1998 Toyota MK 4 non-turbo Supra
1986 Toyota Cressida
1986 Toyota Soarer
1982-1992 Lotus Excel
1992-1997 Lexus SC300
1998-2005 Lexus IS300 5 speed"