I have a 1984 300zx non turbo 5 speed manual that's all original and I would like to keep it that way.

I've done some research and decided the best way for me to get bluetooth in it without ruining the nice 80s aesthetic would be to run a headless stereo system in it much like you might find in a boat or UTV. The advantage this setup will (hopefully) provide over installing a new head unit will be:
1) No new holes or cuts that might diminish the value
2) No messing up the original stereo or speakers
3) Ability to remove it at anytime with very little hassle
4) Probably going to have fun and learn a thing or two

This will require me to run power from the battery into an amp that I'm going to (hopefully) hide in the center console, which finally brings me to the question.

Where is there a preexisting hole that I can use to run wire from the battery to the interior?

There a few places you can do that, but keep in mind that you'll need to rewire all the speaker to work with you new unit and I put the amp under my passenger seat. You will need a pretty small amp that would fit into the center console. I also have a sub in the back and that amp is hidden under the cubby behind the seats.

I did a full rip and replace with my 84' 5 speed NA that I was original owner of, I did new head unit and it looks great, of course single DIN, with kenwood speakers, Alpine AMP, Bazooka tube (I did this install in 97') connected to a 2 into 1 Alpine AMP and now an Alpine head unit, that unit went in in 2009 so no bluetooth. I plan to replace that head unit at some point after all the inventory BS clears, for now it is connected to my old iPOD. The sound is night and day different and frankly you spend the big money on the speakers, AMP and installation of the new wires, the head units are cheap.

I had a power run off the battery and there are several places that you can go through the fire wall.

Thank you for your reply, BadQ45t! I appreciate your input. I spoke with a professional custom car audio company today, and he will quote me on a setup that will hopefully fit my needs. The idea is to completely bypass the stock system. Once that work is done I will post an update in case anyone is interested.

Sounds good, glad your doing it with a real installer, these cars are electrical challenges sometimes, very well engineered for the 80's