Speedometer/Odometer issues

Okay that 5sp is in and seems to be doing great so far. The engine even runs 20 degrees cooler now! thanks to that extra gear so the already worn engine doesn't have to work so hard anymore. (Rebuild is out of the question as long as it keeps ticking and giving up to 30mpgs). Now for my problem.

My speedometer is not the right one for the current transmission. When I still had the old 4sp, the original (85mph head) to the truck had went kaput so I used one from a parts 77 Corolla I had (110mph head). It worked but wasn't the most accurate range-wise due...the odo still worked but eventually stopped turning also. Finding out what speed was what was also a bit tricky. Found a proper replacement (another 85mph head) in the first week of this past May so THAT was nice for a change (1st time in 2 years I had a proper one!).

Now though I have the issue that 45mph indicated is actually about 60 real (figured this when doing a test run of the tranny with a lead vehicle and my keeping pace). The odo also reads way off now...its off by about 1/4 which throws a wrench into mpg checks. (Fortunately my commute has been done enough I can usually get the total to within a few miles...as long as not too many side runs are done). I will be going back to the Corolla head to see if it will work any better this time. BUT! By chance anyone know by chance if there are any aftermarket analog speedos out there that might work properly?

I took the drive gear (works perfectly) from the shot 4sp transmission with the notion of possibly putting it in the 5sp...but I can't remove that one w/o destroying the threads I'd attach the cable to. This wouldn't be so bad if the 4sp spare had this component as well...which it doesn't. This swap from 2 totally different transmissions (models and years) probably wouldn't work anyway. Any hits or help? I'm not totally comfortable with having to "guess" that I'm at the correct speed...particularly since my drive to work takes me through the one town in the US that has the highest cops-to-citizen ratio (not raw numbers) in the US (if it isn't...its real damn close between county sheriff, city cops, state dps, tribal cops, border patrol).

If it wasnt for the fact that my gas guage (the only other instrument in the cluster that works) I'd just as soon find a cluster (one of those where it comes as a unit...sadly) from a mid to late 80s truck.