Spitfire Mk 3 1968 1300cc
I need to know the distance between the inner walls of the coolant jacket gallery on the axes of the frost plugs to ascertain if I can install, permanently, a coil heater in any one of the frost plugs to heat up the engine so that I'm not starting it from cold.
There are a variety of coolant jacket heaters of this type made or marketted by www.fleetguard.com
Can anyone please help me with these dimensions?

Kind regards