Will ANYTHING correct this speedo/gear combo?

[91LXConv]

Well, here's all the pertinent info:
Just swapped stock 2.73's for FMS 3.73's. Ordered and installed purple 21 tooth driven gear for AOD output shaft that appears to be 7 tooth. I say appears because the damn thing is hard to see (may be 8 tooth). This is the correct combo IF the output shaft is 7 tooth. Now I believe it is 8 tooth because speedo is off (reads 75 when it should read 60). I can live with the speedo error but NOT the consequent odometer reading. Using the equation from FMS assuming now that I have an 8 tooth output shaft: I now need a 24 tooth driven gear (no such thing). Is there ANYTHING I can do (I'm not touching the gears, I'm too happy with them!)
Sorry for length, thanks for info!
PS- this is posted on a couple of websites, don't want you to have to reply twice!

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1991 LX 5.0 Convertible:
AOD w/ shift kit, Steeda 3-pc. chassis stiffening kit, 4-pt. AutoPower roll-bar, the K&N, MAC shorties and cat-backs, 3.73's.