I took off the outer half of the heater case, slipped the two heater core retaining brackets off to either side of the core and pulled the old core out. Since I have the whole dash apart, this operation was surprisingly painless. The heater core retaining brackets will not slip over the ends of the new core. ALMOST but not quite. Unfortunately, unlike an F 85, the brackets are screwed against the inner half of the heater case from behind. I really don't want to remove the inner half of the heater case from the firewall if I don't have to, it looks like a pain. Does anyone have a tip for slipping the retaining brackets over the core without taking the whole box off?

The service manual tells you to take the whole box off by removing the screws from the blower assembly and the evaporator assembly. There appear to be some screws attaching the inner heater box to the firewall on the inside of the heater box too that the manual forgot to mention. Looks like an hour or two to take out and another hour or two to put back in. I could avoid that unpleasantness if I could just slip the brackets over the ends of the new core.

 

Never mind :=)
I broke down and took out the inner heater box. It wasn't too bad once I found a bolt on the firewall partially hidden by a relay.

 

This will be the one of the few times one regrets having A/C.

 

LOL. You have no idea how many times I thought that in the last couple weeks.