Hi Derek,
I don’t want to convey that I’m trying to interfere with any decisions you’re making, but paying someone to repair something that you can do, if you have the time & desire to, some basic tools. This is your 67’ 289- correct?
Do you have a handheld multimeter?
All it would take is one light bulb to stay on in the glovebox, trunk, hood, or even dash lights on at the lowest setting to be on, you’d not even see it, a stereo, or an Amplifier, even added gauge lighting, all may drain your battery overnight.
If your reverse lights were accidentally left on, stuck on, another commonly un-noticed issue, that would kill your battery.
If the Alternator is not recharging your battery fully, or if your battery has a low cell, it will discharge quickly. They test both for free at Advanced auto, Autozone. Maybe it had coolant spilled on it recently with the repairs and it affected wires or within connectors, or below it.
If there’s any wiring that’s in need of repair, you can easily do that, too.A great feeling of owning a muscle car is hat you repaired it. If you need help, just ask, that’s what this sites all about.
If you have your reasons for farming it out to another, that’s your choice.
Good luck either way!
-John