New Member with a big question

Ok, heres the situation.

I drive a 1973 340 plymouth duster. I had been having problems with it, but when I let my sister drive it recently, the thermostat gasket went out, the motor overheated and I wound up with water/coolant in my oil. She noticed the car overheating, not by the thermostat conveniently placed behind the column shift, but my steam pouring out from under the hood. Gotta love family. In addition to this, I have some serious leaks in my transmission, I recently had to adjust the linkage which holds it in park, and stops it from lurching in neutral/park, as it was doing both. The transmission seemed to stop acting up afterwards, however I'm not sure as to how well it is now, because I only drove it once before my sister got ahold of it.

My guess, and the guess of the guy at the local shop is that overheating blew the head gasket and/or cracked a head. In addition to this I might need work on the transmission.

The estimate on the motor is 800-1000. The estimate on the transmission is 2000-2500.

As of now, I'm out of a vehicle, which means that I'm out of work. And being that I just turned 20, I only have about 3600 saved up.

So, the basic question is, do you think the estimates are realistic, or over the top. And do you think it is worth it to have the car repaired, should I just have the motor fixed, and hope that the linkage adjustment solved the entire problem, or should I cut my losses and let it go?

I have basic tools at my house, however if the car needs headwork that isn't something I can do myself.

As for the condition of the rest of the car, it was in an accident with frame damage about a year ago, which was repaired, however frame damage is always still frame damage. The driverside rear quarter panel needs to be replaced, and the car definatly needs a new paint job.

As for the prospect of a new car, I can afford a note, as my job pays decently, I just haven't been there long enough to get a good bit of savings.

What are your thoughts/advice? Thanks.