gears & speedo gear in 90 auto

[88mustang_5.0sb]

Here's the scoop. I have a 90 GT that was converted from an auto to a 5 spd. Did all 90 autos come with 2.73 gears or was there a 3.08 option with the Z code (I haven't looked on my door panel yet)? Here's the tricky question...I'm not sure what year 5 spd transmission was put in there. I have heard that if it's a 90+ there is an 8 tooth gear in the trans turning the speedo gear. If it's a pre-90 how many teeth are in the tranny? I figure if I can figure out which rear end I have and which year transmission I have (how many teeth in the tranny) I can figure out which speedo gear I need (cause mine is off). I know the stock 2.73 gears in the 88 LX need a 16 tooth speedo gear cause I just pulled that from another car. Anyone??!!