I've got several brochure pages and specs saved, but with the picture upload dilemma, I can't just drop them here. Shoot me a DM with an email address if you want me to send them to you. Nothing for the '79, but have '72, '77, '82, '86, etc.
Max HP is general 115hp for the 18ft Mariner or MR taking into consideration the weight of the 2 strokes at the time vs your more modern heavier 4 strokes. Mid 80's 90hp or 115hp will be completely fine. I'd say even ideal, but they are a little thirsty and some don't like tinkering with the older 2-strokes. I have a mid 80's 115hp Mercury waiting to go on my '84 18ft MR/Mariner. Other options are really dependent on your budget and desired use/performance. Aside from those Mercs already noted, an older 70hp Johnson/Evinrude triple would be about as small as I'd go and make for a great fishing boat, maybe something larger if you're looking for more speed or planning on pulling skiers/tubes. If stepping up to a 4 stroke, I'd be mindful of weight and probably stay with a 90hp or even drop down a bit. Again, depends on your desired performance. They're pretty light hulls at around 705lbs for the 18ft.
