What kind of tranny? AOD? if it's got a speed sensor and not a cable it's probably off of a T-Bird, cougar, or some other merc or lincoln. Check this out if it's a T5,
http://www.coolcats.net/media/T5info.xls
it will tell you the speed drive gear teeth number, then you might be able to figure out the ratio somehow. I know of a page that will tell you exactly what you want to know, but I can't find it right now, I'll be looking.
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Michael Black
Quantum Motorsports
Norman, Oklahoma
1988 Merc Cougar 5.0 HO, P&Ped heads, 2.25" custom mandrel bent dual pipes, T5 five speed tranny
15.43 @ 91.08mph (not shabby for a 3600 pound car)
60' 2.453 Street tires suck!!!