: Btw, it is possible once the bigger radius is formed to go back . . .

Good idea and there is an easy method. Once the radiused hull-to-bulkhead seam is glassed you build up an oversized square edge from thickened or filled resin, just like a fillet in a seam joint on a S&G seam. The temporary mold for this new edge is nothing more than a piece of stiff tape: masking tape, duct tape, packing tape, etc. Stick the tape to the outside of the hull, lay it so it is mostly horizontal, and pour in the fillet material. The weight of the fillet material will cause the tape to sag a little. That works for you. The actual shape of the fillet is not important.

If it looks like the tape is weak and sags too much, tape a piece of cardboard under it for reinforcement and greater support. Once the resin is hard you peel off the tape and sand or scrape away that sag to give you a straight and fair extension of the hulls lines and shape. If the fillet material is stiff enough you could do the whole thing at one time, but if the material is runny, just do 1/4 of the circumference at a time. Once the fillet has gelled it won't run, so you can flip the boat and do the next section--eventually you get back to the beginning.

Any smears on the outside get sanded or scraped smooth. any glops on the inside can be ignored. They are only visible whenthe boat is in pieces.

Since there will be some kind of gasket material between the two bulkheads of the kayak sections, you would normally have a gap. This extended lip covers that gap. you will want to be sure it doesn;t do such a good job of filling the seam gap that it prevents the gasket between the bulkheads from doing its job--but that is just a matter of sanding and trial fitting.

Take a look at the picture below.

PGJ