Steve,
I did a little poking round on SCOF and it doesn't appear to be a very common failure. One person posted about a failure in 2005 and they ended up replacing the core with an air/heater evaporator from Vintage (no details on PNs used).
A direct replacement from SPF would probably be the easiest route.
I remember when a heater core exploded in my brother's 1965 Mustang...scared the shix out of me.
BTW - 2:48 am...do you ever sleep...starting to suspect you are some sort of alien....
