On Sun, 20 Apr 2008 15:52:39 +1000, meb wrote:

Considering getting and installing a speedometer drive and cable on a
rear wheel to drive a prop for the water segment of a kinetic sculpture
race. Will the old front speedo drives fit on the left side of a rear
axle or is the center hole too small in diameter to fit on the rear
axle?

Probably too small - typical front axles for which those mechanical speedos
were made had a 5/16" or 3/8" diameter. However, as I recall, the centre
parts were just cheap pot metal and you could probably easily drill or ream
the centre hole to suit.

You may not get much torque before failure out of such an arrangement.