[Steeveedee]

As for bypassing the heater hoses, you can plug both ends at the engine with some purchased items, but I've jammed the 5/8" hose onto the 3/4" fitting when the heater core split, to make it home.

It'll be much more fun to do that work with the engine out, and in fact, if the right side fender and wheelhouse were off, it would be even more fun. You have to balance ease of the work- fender and wheelhouse off, or not.

If I were in there working on it on my own vehicle, I'd replace the heater core. I don't know that it has ever been replaced. HOWEVER, unless you have determined that the evaporator isn't leaking, and if the heater core isn't leaking, I personally would let sleeping demons lie.

My approach would be to install the other AC components and see if a good hard vacuum can be drawn and held to the spec. If that is the case, you don't need to go into the box after the evaporator or heater core, unless you just like needless pain and work. That might conflict with having the engine out, unless of course you install all the other AC stuff before taking the engine out, which really isn't all that much more work, on and off, since you can pull the compressor and hoses to the side when the engine comes out.