Mansfield/SeaLand 751/752 obsolete for 20 years
The marine division of Mansfield Plumbing was sold to SeaLand Technology in 1984...SeaLand made the 751 and then the 752 for only a couple of years, and then discontinued both...discontinuing all parts support for both versions by about 1990. So even if you could find ANY base that you make fit it, the rubber parts in the pump have to be at least 15 years old...so worn by now that it wouldn't be worth the effort. It's time for a new toilet. Take Steve's advice...buy a Raritan PH II. About $100 more than the cheapest toilet, but worth it if you want a reliable trouble-free free toilet. The PHII has been rated the best manual toilet under $500 for decades. If space is tight, the PHC is the same pump, but on a compact base.