I found this number (1685) on the wooden part under the front seats.
Is it a part number or does it some other meanings?
You can check floorboard part numbers in the Master Parts Reference but you need to identify your car. I took a quick look and I think you might be short a couple of numbers preceding the 1685. Sections 23E to 29D depending on Q,U,30U, 2dr. 4 dr. coop sedan etc.
Thank you Chet I will check the Master Parts Reference.
Do you know the original thickness of the plywood in the roof (1/8"?)
(1929U 2 door sedan)
If the 29U 2 door Sedan is anything like the 29U 4 door Sedan the roof is not plywood. There is a slight arc left to right and front to back. I don't think you can accomplish this with just plywood?
Below is a picture of crazzydave's original roof. You can browse his pictures in the "Off Site - Photo Gallery"
(http://www.1948plymouth.info/galley/var/resizes/Crazydave/-Plymouth/20150221_175001.jpg)
The car has a plywood in the roof maybe change some time?
Most original cars I have seen are bows and slats. If the plywood will work and is easier to do, go for it, once covered nobody knows.
Chet...
Yes maybe nicer with original layouts.
I think this was modified late 50'
The roof, how it is done? Is it vinyl with padding?
I think whatever they use on the Model A should work fine. The same goes for the rain channel. I want a leak proof roof so I will have a professional shop near me do this. I haven't decided yet.