Firewall separation from Cab, Wot have i missed??

I have a 1937-38 Inter D15....supposedly a flat back cowl. There is joint material between the cowl (firewall) and the cab. I need to remove the cowl, cab & joint material so I can check for any rust that my be present prior to blasting & painting etc. I have undone numerous bolts around the top section (dash) and down the sides, as well as mounting bolts to chassis. What have I missed so I can pull the bits apart?

Mike

Add a photo so we can all see what you are trying to do.