Rachel4291, welcome to the board.
There really has not been much stuff that has changed in all the years since the original post, except maybe some of the original suppliers have closed up shop, and most of the few pictures that were here are long gone. At the same time, a few new suppliers have stepped up, but for the most part, Street rod Mopars haven't changed much.

The story is still the same. Before we can give you any worthwhile advice, we really need to know a little about your abilities, about the condition of your car, and most important what you expect the car to be able to do when you get doe with it. Having an idea what your build budget looks like is also helpful.
Please understand, there is a world of difference between building a really nice highway driver and a 1/4 mile terror, trying to do both becomes a build with a long list of compromises and often results with an unhappy builder.
Budget is a huge concern. These toys are not a cheap undertaking. The hard cold reality is that unless you have a big pile of parts laying around and have a ton of building skills, tools and equipment, its nearly impossible to get one of these old rides on the street safely for less the $5,000, and then it won't look pretty. Expecting to be able to build one for less often results in another unfinished project. I'm not going to sat it can't be done, but the odds are not with you.

So lets lay down a few basics. Your 39 Dodge started life with a boxed frame a semi modern independent front suspension. This suspension was used with very minor changes up through the early 50s. The original brake system was ahead of its time and were among the best available, in 1939. As good as both the suspension and the brake were, they are painfully inadequate for modern times, unless you live in an extreme rural location where sudden stops are never required. Both can be upgraded to acceptable standards unless you intend to daily drive in heavy city traffic. The original flathead 6 or flathead 8 actually moved the car fairly well, but were not high performance. Don't even think about adding more power without upgrading both the front and rear brakes.
The original cars came with really big steering wheels. If the greasing of the front suspension was kept up with, they really did not drive bad without power steering. One worthwhile note here, the original steering column is part of the steering box, that shaft that holds the steering wheel is a 4' long 1" diameter steel shaft inside a 4' long 3" diameter tube that will not collapse in a crash, it can go right through you. You can cut both shafts and add a modern top 1/2 of a collapsible column with modern turn signals for a huge improvement in safety. Adding power steering is a pain with these cars. The Cavalier rack and pinion with (or without) power steering can work, but it requires effort to make work.If power steering is a must, upgrading the entire front suspension with a modern clip, or a Mustang II front suspension is a better move.

I've only built about a dozen 39-48 Plymouth/Dodge cars in the last 20 years. I've discovered several places where parts can be had, and some stuff (like sheet metal) is very hard to find. If your looking for parts, we need to know specifically what parts you are looking for. If your changing all the suspension and brakes, telling you where you can get those parts is wasting both our, and your time. It is amazing how many mechanical parts are still available, but if your looking for floor pans, you need to learn how to form sheet metal. Gene