Okay, so I am hearing that I'm the Wile E. Coyote of preglow relays?
I had a Ford solenoid arrangement on my old Coupe. My biggest drawback is that I don't want to mess with the interior of the 300d by installing a switch.
The other option is, of course, one of Funola's modified relays.... Which keeps things closer to stock but still requires a switch somewhere.