Keep your eyes out for a Yamaha.
3 cylinder 25 would be ideal (basically a de-tuned 30hp). But a twin cylinder twin carb 25 is a really lightweight motor that, if cared for, is one tough motor. And don't discount a good 4 stroke 25 either. That is what I have and I wouldn't go back to a 2 stroke unless I was paid to. Mine's on a 548 LDV War Eagle. Love that rig. VERY little maintenance is needed and by far my favorite boat I've had, and I've had a bunch. Funny, I was talking to my dad about it the other day and he was saying that he thought I'd never get rid of the 14 footer (1432) that's got the old evinrude 9.9 on it. I kept it-still got it actually (I gave it to dad to use) but I hate the recoil starter, I hate how slow it is, the throttle linkages are worn out, and I drown in smoke when I fire it up the first time. Owned it since it was 2 months old, 1984 model, about 25 hours run time on it total. We never used it much other than idling onto the and off of the trailer and that's about it. Clean the carb twice a year, which is a pain in the butt compared to most of the Yamaha's I've worked on. Last time I had dad's on the lake, I had to put a rope on the starter....hate that design. And that little thing is tough to start via rope starter. For whatever reason, it seems like it's got 500 psi compression. Gauge says 120 on both. Also had an older 25 johnson, hated it too. Single carb/twin cylinder. Rougher running than I'm used to, liked gas, liked to be fixed from time to time. And smoked horribly when it was cold. Once you made a wide open run, it'd clear up and was good to go all the rest of the day, but sometimes I didn't get that opportunity to run wide open (stumps, rocks, etc). Always had to carry some extra spark plugs. I actually traded that thing on the water (well at the ramp)...guy in anotherhboat had a 25 Yamaha twin cylinder twin carb motor that sat for a long time, he commented how clean the Johnson was and I told him I'd trade...jokingly...and he said ok yeah. The Yamaha ran perfect. And being it was a 100:1 fuel/oil mix, lot less smoke.
I saw a 25 triple (3 cylinder) Yamaha with a Panther PT&T on another site for $3,000...surprised it hasn't sold yet. Sometimes you can drive a little and pick up stuff cheap. 25's in this area are gold because of the public hunting areas' 25hp limits. I had 2 of the 4 strokes, kept one, sold the other the same day it went on CL, $2400. Elsewhere in the country, it'd have been a $1000 motor, at best. The other side of that deal is that a lot of the used 25' s are used up. The flooded timber takes it's toll. Skegs busted, bent/broken props, foots that are destroyed, etc. Another advantage of Yamaha, the shift dog pin in the foot is cheezy...little 5mm piece of steel, it will break if you hit something hard enough, and it gets hard to shift into/out of gear. Takes 10 minutes to fix it due to the design of the foot.
the older points ignition motors are headaches, unless you know how to work on 'em and keep 'em running. Most of the Chrysler stuff needs to be in the scrap iron pile. Some guys still collect them, though.