Heater core replacement in a 69 396 w/ AC

[Longhorn Paul]

Had my new best friend gone over by someone qualified to turn wrenches. She passed, overall, except they discovered my heater has been bypassed. I'm told this likely means she has a leak.

Question: is replacing the heater core something that someone with modest mechanical skills should attempt or should this be left to the professionals.

If left to the pros, does anyone have any idea what it might cost and a general idea of what's involved?

I did scan over the archives but it seems most concern heater core setups in rigs without AC.

Any help / advice is appreciated.

Paul