Greg Anger

Hey everyone I have a 02 Sierra 1500 . I got 320k plus out of my 4.3 vortec. I put in a 1989 305 small block chevy into my 02 sierra its running great but the problem is that the transmission also has 320 miles on it. The 305 is at FULL potential... but the (computer controlled tranny SUCKS ) ... so i have a rebuilt turbo 300 thats going in ( not computer controlled) . My question is do i have to get a new speedometer ? Or do they make any kind of cable that can keep my old speedometer working like it is with the mechanical turbo 300 tranny ? This might be a shot in the dark but if anyone has any suggestions on were i could find any info would be great...