It should be possible to swap the movement, and a 6r15 or 4r36 would drop in. There are a couple of things to be mindful of. Firstly the movement holder needs to be the same thickness; they're different for movements in diver watches. Secondly, the date wheels must be for a crown at three, not the crown at 4.
Swapping the movement holder is an option but that involes partial disassembly of the dial side of the movement. You might have to do that anyway to keep the day wheel as the donor movement might not have that.
Swapping the crystal would be a doddle and is just a case of finding the right size (width and depth).
Your biggest problem though will be sorting out the best crown/stem that would work with that watch. Unfortunately the 7s26 stem doesn't fit the more advanced movements, and not all stems from existing watches are the same lengths.
I wish you luck.