With a (per sailboat data website) 8500# displacement and 22 feet of static waterline, there is a definite upper limit to the amount of HP you can utilize. There is the limit (sort of...) to how much speed you can generate once you hit "hull speed", and my SWAG is that you might max out at about 6.5 for a top maintainable speed in smooth water with a clean bottom.
The displacement, OTOH, puts you up there with 'bigger' boats. After all, my Olson displaces only 2K # more. Our boat was spec'd out with a 23 hp diesel and when I repowered I went with a 25 hp diesel. This seems fully adequate, with a bit to spare. Beyond generalizations, it's hard to compare our hulls, with ours being much flatter aft, allowing more speed due to a more WL.
As for the common inboard used by a lot of boat builders in the 60's/70's, the A4 gas engine, it came in a couple of HP ratings with 30 being very common. My guess is that if that engine had been 'rated' at 20 HP instead, no one would have noticed any difference in real world usage.
Apologies for pontificating.... and really, I betcha that any modern diesel of about 20 HP would be 99.8% adequate for the E-29. Something like the Betamarine 20 is often pretty easy to "fit" into a boat, as well. It's a more compact block than earlier designs.
Keep posting, and let us know how your idea spools out.
As Red Green used to say on his wonderful TV show: " Keep your stick on the ice, and we're all pulling' for ya!"