Yes, I do believe someone sells a box that takes the signal from the electronic pickup and then with an electric motor of some sort turns the cable going to the original spedo, but they are quite expensive if I remember correctly.

I think you can find the parts to convert your T5 to mechanical cheaper and more reliably than you can get the magic box.

•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-