To start an answer to your question...it depends on what it's being put into, what your running for an engine, if you are contemplating towing, the Ring & Pinion ratio, the tire diameter you plan to run, and what speed you intend to "cruise".
The most popular T5's are from the mid-80's S10's from V6's with a 1st gear ratio of 3.76 and a final OD ratio of .72. They have 14 splines on the input shaft. These are classified as non-world class (NWC) transmissions and T5's up to 89 were mechanical speedo's, which are preferred. There are also World-Class (WC)T5's from Camaro/Firebirds that require a tailshaft modification to relocate the shift tower. These are differently geared (closer ratio) have a 26 spline input shaft and are normally more expensive to obtain. Most NWC T5's from a j-yard are priced from $150-250 and are identified (year/gear ratios) by a tag mounted on the Driver's side of the transmission. A typical 85 T5 TAG will read 1352-145. The numbers cast into the T5 case do NOT identify it's year or ratios.
There is a wealth of information on T5's in this site and "Inliners" (using the "SEARCH" function)which points out the necessary modifications to install behind a "bolt" and there are numerous folks that have successfully completed the installation.
Be advised that this is not a pure "bolt-on" install and although the modifications are relatively simple, it is not something to rush into without a GOOD DEAL OF RESEARCH.
My T5 install was relatively easy but you must do the modifications as outlined and should pay particular attention to selecting a R&P ratio that let's you maximize your T5's potential and meets your own personal needs.
The T5 opens up the potential of the little Chevy 6 and makes driving a real pleasure. I hope this helps getting you started on your journey.
