New to Forum & Owning a Truck - Q's

[Philadelphia]

First of all --- Hello! , My name is Larissa, i live in Yellowknife, Northwest Territories Canada... And i just bought a truck I have never owned a truck before, but i fell in love with this one, and for the price it was a steal of a deal. The truck was very cheap, and has not been on the road in 12 or 14 years. It was written off in a rear end accident 12 years ago ( minor damages but at the time, worth more than the value of the truck) and It needed a replacement bumper/rear tail gate and exhaust. The previous owner had taken it off the road because he did not have time and i guess was saving it for his son, but they found out they have to move so he had to sell her. I don't have many pictures, just the ones of me towing her away from her old owners with my camera phone.

She is a 1976 GMC pick up? 350 CID 4BBL carb, 2 wheel drive. and standard/Manual ...(lots of question marks see this is why i signed up to find out more, it has LOW, 1, 2, 3, R)

I think this truck is a hybrid truck, that's what i call her anyway, the side fenders say custom classic, the dash says Scottsdale and the paper and registration say C14? So i'm not sure what or how many trucks my truck is. All i know, is the body work has been done mildly, lots of bondo on the bed, but the floors have new sheet metal riveted in and the door skins etc have been done.
The previous owner was gutted that he had to sell his truck, and his son was a little upset it was going to a girl, but i assured them it would be in good hands. From what i know, the engine was rebuilt and only had about 2000-5000 km on it when it was parked.

One question that i am curious about right now is :

I would like to replace the Carb to get better fuel mileage and hope that it might be able to run in the cold winters here ( can get to - 50 easily in winter ). I would like to know where i can find one that will perform well and be well crafted i dont want to buy something that will break in a year. I also wanted to know what exactly i need to look for the fit my specific engine.

Another would be, what is the bolt pattern for the wheels?

Here is the only picture, sorry for the terrible quality