never done it myself, but I know it can be done.
I doubt you will be able to use the existing cable because it will most likely be to short to reach the handlebars with enough slack to allow for turning.
I've heard there are alot of speedos that will work on the Savage. Not sure where to purchase them.

I have a bike speedo on my LS650. It's not spot on much past 50mph. If you want to try it make sure the one you use it accurate before you take off the stock one. Plus you have to keep in mind that you will loose your odometor. I put on the bike comp to keep track of the 100 miles with it's re-set-able trip.

I put a Acewell model 2702A on my savage. It has speed, tach,trip1and trip2 meters,and turn signal indicators. This unit uses a magnetic pick-up on the front wheel.

The Acewell unit comes with all cables and wiring. The only thing you need to purchase separately is a mounting bracket for the handle bars.

Try electrosport.com then click on speedometers, then click on street. Should be the first unit you see.Good luck