78 speedometers

[Hantke]

So my buddy has a 78 shortbed stepside C10 W/ a 350 V8 and a manual transmission, well, the dash was originally setup for an automatic so the speedometer doesn't work with the manual transmission in it now, so if I was going to fix the issue, would it require a new speedo cable and new speedometer? I haven't looked at it yet because he shipped out a while back, but being in fairly sound mechanical condition I think it would make a great little truck to play around with.

Would I be best replacing the speedometer and cable, or is there an adapter or something? Whenever I try looking it up I'm finding clusters for sale, but not the info I need.

Thanks!