1984 gmc pickup

It is. Just go get some brake line and bend it to fit. If you get a long length and have to cut it to the required length, make sure to use a double flaring tool to make new flares.

My question is, do they sell the brake line already pre bent,

Yep the dealer will have it all preformed with the proper fittings and clips. So will a GOOD parts supply shop.

or do I have to bend it myself?

You can if you want. You will need a proper double flaring tool, a tubing bender, tubing cutter and the correct line and fittings.

Also is this a dealer part, or would any parts shop have this

A LOT of the lines on a vehicle "look pretty standard" but it doesn't mean they are.

If the line broke due to rust then you might as well pull both of the front lines and replace everything including the rubber lines. it will be cheaper in the long run and MUCH easier. I would also consider replacing the rear lines as well if you haven't already.

Thanks again Mike. I bought a new brake line which came straight "without bends", and the ends flared with fittings already assembled at both ends. I bought a 12 inch, because that was the same length as the one I broke. I used the old brake line as a template, and bent the new one as close to the old one as possible. I had a hell of a time trying to get the thread started at the end that go's into the front proportioning valve. It was in a very bad location, inside the frame rail etc etc. I ended up taking the bolts out of the proportioning valve, moving it enough so I could get good access to the hole where the fitting go's in. I still had a problem getting the new brake line in. After literally 50 attempts, I finally got the thread started. The rest of the job went fairly smoothly. Any idea why the new brake line was difficult to get in, yet when I tried to reinstall the old one, it would go in no problem. I made sure the fittings between the new and the old were the same by attaching a nut to both. They were the same. Have you ever had a similar problem.....thanx

Yup. It only takes a very small amount of mis-alignment in mating the threads to cause you a world of grief. It's common enough when bending your own lines to have to tweak your bends a bit to find that perfect alignment. Glad you're back in business.