Looks like you've got a check valve plumbed in line. Just making a suggestion to read up on check valves in saltwater applications. They tend to fail due to calcification build up and offer you a false sense of protection. I've never used them on my systems.
If you like that pump, you should be able to go to a plumbing supply buy a Grundfus pump, remove the 4 allen screws pull the front flange off and install your plastic one. The only thing would be if the empeller is different. They still make that small pump i beleive but most places dont carry it they just carry the 3 speed pump. But i think the bolt pattern is the same.
Not 100 percent this would work but i think it would. It may be worth a shot the pump is like $75.
I looked to see if i had one of the small ones, i remove them sometimes from new boilers and place something else in but i dont only have a 3 speed.