yah that tach won't work on your bike, the 8, 6, & 4 are refering to the number of cylinders that it'll work with.  Back in the day I had a '81 f150 that was a stick, so when i got it of course i wanted a tach, well found that out after i installed it what that little switch was for.  I didn't even look and left it on 8 and couldn't figure out why it wasn't reading right.  Actually read the instructions and saw that it needed to be set on the 6, beings i had an inline 6 cylinder.  So to clarify through all my rambling no it won't work on your savage.

I just looked on Drag Specialties website and could find the DS244133.

I am sending them an email to find the replacement part number.  I vaguely recall it was around $80.