Did you by any chance take the speedometer needle off to get your new odometer barrel in? The needle is very sensitive and when taken off it is easy to get damaged or miss-calibrated when puting it back on. Since you say it skips around, it sounds like it could be damaged <img src="/forums/images/graemlins/frown.gif" alt="" />

When I did my cluster swap, I didn't take the needle off, I just drilled some brackets out with some small drill bits to get my odometer rolling <img src="/forums/images/graemlins/lol.gif" alt="" />

http://www.scerbfab.com/carb_faq.html