Cowl on 29 Auburn

We owned a 1930 Franklin with a Dietrich body had the cowl spot welded to the firewall (and had a whole bunch of other constuction that was prety advanced as well - ex. aluminum castings that people cannot figure out how they were done as they were so precision and so complicated.

I am replacing significant sheet metal on the cowl of my 29 Auburn, but I want to keep the firewall intact. I don't see any obvious spot welds on the flange or lip of the cowl where it attaches to the firewall. Any suggestions on how to separate them? If I sand the paint to the metal, will I see spot weld patterns or did they even spot weld back then?