khofmann-
The hp advice so far is very good. Max is for a single or twin operating engine(s) at one time.
There is NOT sufficient room for twins on the transom of the Classic CD-22's (Pre-1987).
The Pre-1987 C-Dory Classic is rated for less than the 100 hp used as an example (only),. The boat was designed for a 70 hp 2-cycle engine of about 250 lbs. or so, but a 90 hp 300 lb 2-stroke was also considered OK.
We have seen up to a 115 hp 4 stroke engines weighing close to 400 lbs mounted on these boats, but generally a 70-90 hp 4-stroke is best, which weighs about 370 lbs, typically. You'd only need more hp if you frequently carried very heavy loads and were concerned with maintaining top speeds for safely outrunning bad weather. A 115 hp engine on one of these boats would require large trim tabs and very careful and skillful managment from the helm to use without getting into trouble.
The Classic hull is absolutly flat on the bottom (looks like a clothes iron's bottom) and handles well in chop and swells at moderate speeds, at slow trolling speeds, or at rest. As the hull becomes overpowered, it becomes a bit difficult to manage and is somewhat unpredictable. This is also true of the 1987 and later hulls, which have a shallow modified V bottom, but to a slightly lesser extent.
Your best course of action would to use a single and kicker combination.
The main motor should be from 70 to 90 hp. A 4-stroke will be best, although an Evinrude etec direct injected 2-stroke would be about 75 lbs lighter, which would be marginally better in ride characteristics.
I'd stick with a four-stroke kicker motor, from 8-15 hp. Personally I'd get a High Thrust motor with 8-10 hp or so. The High Thrust motors have larger lower ends, bigger props, and lower gearing for better energy and momentum transfer. They're more rugged, overall.
I'll leave it to others with this type of set up to discuss what type of kicker motor mount is most suitable for the Classic 22's transom at the side (outside the motor well). Controls are also another issue to be decided upon.
Good Luck!
Joe.