Welcome to the site, Tony!
It looks like you've found a very nice car to work with. The only thing better than a 340 is a 340 with a 4 speed! As for your gauge problems, chances are the speedometer cable is either broken within the cable housing or the speedometer gear is stripped out in the transmission. You should be able to at least get the speedometer working again relatively easy, but the others will need to be tested 1 by 1 as suggested to see if they're getting a good voltage. If you don't want to tackle it yourself, you could remove the dash and send it out to get the gauges redone/re-calibrated, but that can get pricey.
