I know my situation and solution is not exactly the same, but the idea may work..
Look at This Picture
My starter uses an air valve to engage it, so I made a simple adapter bushing to screw the original cast starter button with 3/8-24 thread onto the 1/4-20 stem on the air valve.
Right now it's temporally attached to the flywheel housing, but when the cab is in place it mounts to and under the floor with two screws.

Is there a similar electric switch that could be attached to the floor and adapt the cast button to it, no linkage necessary?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-