I am brand new to the Forum, and need some guidance from you Pros…in HO, I enjoy rebuilding and running the wood/metal cars of Varney, Silver Streak, even Megow (late 30’s andpostwar.) EBay supplies the cars, Mostly junkers, and I am constantly searching for parts, sources, and other people with this wierd take on the hobby. If anybody out there shares this interest, or knows of a thread to access, please let me know.
Well, it’s not my primary interest, but I’m a Scot. As a boy in the 60s, I picked up a number of old, old cars in a box-of-trains at a yard sale. Some had wood floors, and thin metal bodies. Until 4 years ago, they all lived in boxes and got carted from attic to attic for 40 years ago. Not one has been thrown away.
I too love bringing these old cars back to life. Tonight, I resurrected an old Mantua hopper and a Crown tank car. Admittedly, these were plastic cars, but they’re now equipped with Kadees and running behind modern DCC-equipped engines.
I’ve got a few old ice-bunker reefers with the thin, sheet-metal bodies and wood floors. The Pabst Blue Ribbon car is on the layout now, parked in front of the icing station awaiting its next load. I think there’s an old Borden red-white-and-blue car in a box somewhere, too.
Really, all it takes is a Kadee coupler, spring and draft gear box. If the trucks are in good shape, clean them up and maybe add a bit of oil. You could add some grab-ons to improve the model, but I’m not sure they’re worth that much trouble. Instead, run them as “background cars” on your train. And remember how much you loved cars like this when you were a boy.
I really like my old Globe / Athearn metal cars and have real miles on their wheels running on the layout. My favorite is the ALL METAL, Athearn 250 ton crane first made in 1951. It is very heavy scale model and rides on real sprung Buckeye trucks. It’s restricted to 25 MPH on the layout just like the prototype was. 
Yes I do have newer cars and locomotives on my layout too!
Nothing wrong with the classics. On the real oldies, with the pizza cutter wheel flanges, a set of new metal wheels will bring them right up to snuff in the running department. Convert the couplers to Kadee (or whatever you are running) and weight up to NMRA recommendations (one oz plus 1/2 oz per inch of length) and you have a car that runs as well as anything out there.
Appearance of the cars can be improved. Paint and weathering makes a car, more than any amount of kitbashing and super detailing. If the existing paint job is hopeless, you can repaint and redecal. A rattle can of red auto primer gives a fine box car red . The underside of cars should be painted, a quick spray of light gray auto primer (after masking off the topsides) makes a surprising improvement in over all looks. The glossy sheen of molded plastic (wheels, roofwalks, ice hatches, trucks, etc) needs to be covered with a good flat paint job. A brush works, the model railroad paints will level out and conceal any brushmarks. If the entire car is too glossy, spray it with DullCote. Wheel faces on friction bearing trucks are covered with oil from the journal box, I use grimy black. Trucks should be rusty iron color, not glossy black nylon.
Weathering is a whole nother subject, I’m not all that good at it, so the only advice I can offer is to practice on some cheapo train set cars that you don’t care about.