I am wondering if that radiator is for a flat faced cowl or utility body. That might move the filler neck inside the vehicle. I also thought about a COE but that seems to move the filler neck so that it would be less accessible. Also, consider industrial applications.
Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix