Need advice on priorities

[DoubleL]

Okay guys I need some advice. I just sold my Daily driver so now my '66 is my only rig. I drive 25 miles round trip to work. I have replaced all hoses and gaskets, full tune-up, new belt and oil change. Basically I have been prepping it to drive on a regular basis. Here is my dilemma:
I have a few bucks to put into it (about $500) right now. I will be able to gradually put more into it. I am trying to prioritize things right now. Here are the things it needs:

The rear end = it's howling pretty good at 30-40 MPH ( I know of a 3.73 Posi I can get a hold of for $400) I don't know if I will install by myself yet.

Tires = Legal tread but barely, definitely not driving them through winter. Thought about buying used to make do.

The other Stuff = Gas gauge isn't working properly, (not fun) speedometer cable broken ( replaced with new and broke new cable within 50 miles) Doors have no key, (can't keep valuables inside) heater only works on lowest speed. Couple of small but bad rust areas.

Any ideas, opinions?