Long story made short. The key to the '51 truck is hidden/temporarily lost in the shop, can't find it (but will in time I trust). So, rather than having a new key made I'm thinking just wire in a simple on/off switch at the back of the ignition switch until the original key turns up. Just checked my inventory and all I have is a new 120v SPST light switch. Any reason this won't work?
On the good news front, a decades-long delayed shop cleaning and organizing effort is underway.
Thanks, RonR