Easiest way to add a trip meter is to add a bike (bicycle)computer, which also gives you a speedo, hour meter, and all kinds of other functions. Some have a compass, which is also nice. The bicycle computer is totally separate form the rest of the cycle. You can even keep your stock speedometer in place (or yank it to make a great in-tank cup holder).
The sport bike guys swear by the Sigma BC800 -- eBay has several for $15-$30. BC800 is accurate at motorcycle speeds ( to 180 mph - something the Savage would never see). Most bicycle computers won't accurately display over about 50 or so.
Here's a little article with pics:
http://www.canyonchasers.com/shop/generic/sigma.phpHere's the manufacturer's website so you can see what the computers will do:
http://www.sigmasport.com/index_usa.htmlGPS is also an interesting idea, but more $ and takes a minute to aquire satellites.
Last resort is to go with an aftermarket speedo, which likely will not fit the tank opening. They have them to mount up on the handlbars. I'll look for a web link...