I think for Historic / Mot free status there must be no significant changes in the past thirty years, if the engine conversion was done thirty years or more ago you should be ok.
On a bracket bolted to the bulkhead above the brake pedal, when you push on the brake pedal the plunger is released making a circuit and the brake lights come on.
If the switch faulty your brake warning light can come on.
If you do decide to tow someone out of the mud, make it very clear to them ( video it on your phone ) that any damage to their vehicle is their responsibility.
You could possibly pull something off their vehicle.