[A Cobra guy]

Go for the street rod type heater core. Mine came from E-M but I'm sure it was a 3rd party part. It is about a 6inch cube with a 2 speed fan. Louver doors on 3 sides can be opened or closed to let heat into the cockpit area. The more you close them the more heat is diverted to the defrosters. I have the cast louvers which I think look good. I know you have a glove box in your dash. Mine is very shallow on ther left side to make room for the heater core. I don't know if E-M had 2 glove box inserts but if not that material will be a lot easier to work with than makeing up a heater core from scratch.