Cleaned up the firewall and welded in a patch for two holes I assume were for the cable option on the the deluxe version but were just leaking air now.
Cut out the section of the heater and mounted the new core fits great A new heater blower motor was installed and really puts out some air...and dust from the ductwork. Heater switch still works and I have all three speeds WAHOO!
The old core before cutting
the bigger deluxe core