i needo a speedo

[steve]

so i have an 83 c20 with a 350 and i just replaced my old busted th 400 with a slightly newer 700 r4, but i realized that the th 400 used a mechanical speedometer and the 700 r4 uses an elecrical one.  i was wondering if there are any apapters out there i could use or if i'm just better off getting a whole new speedo.  and any good deals you guys might know of would really be appreciated! thanks

[Captkaos]

700R4's came with mechanical speedo cables, you need the mechanical gear set out of one,
What year did your 700R4 come out of? 88-93?
This is what it looks like:

[steve]

i'm not 100% percent sure but i think it's an 88.

[Captkaos]

You can get the mechanical pieces from any transmission parts store, being an '88 it would have the electronic VSS.

[steve]

do i need to know any specifics about the car before i buy the gears?...tire size, rear end ratios anything like that?  and once i have the gears in the tranny do i just hook up the old speedo cable to it?