I tried the same thing on my 48 Ford Woodie and the best way to figure an approximate date is by using what you have. Check the glass. If it is original, that gives an approximate month. I don't know about Mercury serial numbers on the body but on my Woodie, the body stamping (also on the firewall) tells me it was 146 off the line based on the start and end of production of serial numbers that were stamped on Woodie bodies. Perhaps it is the same for Mercurys.
