[a.c.ward]

vic, we did a connect and cruise on a customers car and experienced similar speedo problems, we used Dakota Digital gauges, so I cant help with the gauges, but check out the following information I found on line:
Circuit # Position Wire Gage Color Description
818 D 22 Brown Vehicle Speed - Out

description in manual of what the brown wire does:
Vehicle Speed (BROWN) – This is a non scaled output for use with
auto-scaling speedometers and will not function unless a vehicle
speed sensor (VSS) is connected to the ECM through the VSS wire
in the harness.

this in on the 12 pin connector engine side of the harness. I connected this brown wire to the DD box and speedo worked, maybe worth a try for you.

maybe check out also

circuit #121 position 25 wire gauge 22 wire color white engine speed bulk head pos c on the blue C1 engine connector, also shows speed out.

if you have any further questions or need to talk this thru, you should still have my number, we talked thru the Vintage Air hardlines once before, if you need my number PM me.

AC