Use an early Ford V8 starter solenoid and a starter button. Takes a mod to the starter or the stock A starter switch to mount cable directly to starter contact.
Also, you'll need to replace the copper contact lump with a stud...Drake's catalog shows 2 versions of V-8 stud reproduced. There useta was a kit for this that mounted a V8 solenoid on a special bracket right on the A starter...I think from memory mine is just set up to bear against that copper lump, but I would prefer a bolted connection to a cable.