My friend and I put a v6 speedo cluster into his v3 RA, we fitted a Motec ecu and fitted a v6 based engine at the same time so no sensor issues
I used the v6 clock loom and spliced this into the v3 loom, (also needed was an electric speedo drive from a later car) everything works as it should do, even the fuel gauge, which I thought we may have issues with.
The hardest bit of the job was to physically fit the v6 clocks into the v3 dash as the surrounds “curve” in opposite directions fortunately this job went to my friend and I got to do the wiring ;D
Edited to say I couldnt find a correct diagram for the v3 dash so ended up examining and "buzzing out" the clocks and making my own