Back to report that We did It!
One hatch has been done successfully!
Believe it’s a size 20. Our end
game is to replace the hatch lids with spares off Defender but the actual hinge bit with the roll stop is part of the assembly that stays on the deck. I did indeed have the rollstop kit from Lewmar. It states to “punch out the existing pin” - nigh impossible with the flanges on both ends of those
steel pins. We bought a cobalt drill bit and held one end of the pin in place with friction from a flat screwdriver, while drilling out the flange on the other end.
Putting in the new replacement “roll stop” was a whole other story.

There is a rubber strip which sits under a plastic piece inside the deck side of the hinge. The plastic sticks out and locks into the “gear like” grooved side on the lid hinge. The rubber is soft enough to deform under force and allow the plastic bit to move down & then up to lock into the next slot in the lid hinge. This is what allows the roll stop to lock in various positions. Using these kit
parts as is, however, it was impossible to get the new pin in!! The rubber and plastic pieces push so much against the upper lid hinge that we couldn’t get the pin through. Luckily before trying to force it further we checked for alignment by getting a screwdriver shaft through one of the hinges & to check how the new roll stop would
work. It was too tough to open even a crack and we ended up having to cut off about 1-2mm off the stock rubber piece height before the force needed was reasonable. The trick to reassemble ended up being to get the pin in through one side and keep hammering away until it knocks out a plastic end piece (shaped like a keyhole) on the other end...then push down as much as possible on the hatch while another person uses a towel and vice grips to squeeze the final end piece back into the slot and on to the pin.
Phew! Tougher than expected but feel way more confident about the next hatch. Hope this helps someone!!