I think the rudder castings on the Wave are a little newer, there are some fitting issues with the gudgeons depending on 1 piece or 2 piece. Just double check before you buy-shame the style you are looking for, post 87' w/ Miracle-20 connectors to the crossbar are also the most expensive and darn near impossible to find used. There's a reason your boat was cheap! I might suggest the EPO rudders as well, they are a fair bit nicer feeling than the plastic variety.

Be careful modifying mainsheet systems. If it feels unhappy it probably is. We blew up a 8:1 mainsheet system adding a 9:1 purchase block while offshore in a leg of the Tybee 500 (I forget which, we broke a lot of stuff) on the N20. Harken was fantastic and replaced the damaged bits but I recommend using as designed.