Would like to build my own one of these https://weedersdigest.com/shore-restore-portable-boat-float-mounted-dredge-system/. Can anyone tell by looking if he pump head on this thing is some kind of off-the-shelf macerating pump of some kind? 5k is just a bit too salty for me for this capability. Thanks in advance!

hard to tell, but looks like a septic macerator head ... unless this guy owns a casting company, I agree with you that its a part off some kind of sludge pump.