Thinking of tackling the replacement of the heater core as well.... I so far have removed the middle console and fan, it looks pretty tight under there. Any quick tip of getting to it?

Its a pita, but can be done. I removed my entire dash whe I replaced my heater core, but thats only because I was going to do some rewiring in the dash. Im sure the 260z and 280z are a little different, because IIRC, the 280z and 260z have different heater cores.

But, on mine it looked like the heater core could be removed just by removing the blower motor, and the metal adapter thing bolted into the firewall.