BoatBanter.com - would a smaller motor fit?

I suppose you could call this boat a runabout model.

hi there,

I've been tinkering with a 1972 80hp merc that I got some time ago that
started, but has since failed to. It appears there may be a problem in
either the switch, and / or coil. Based on the prices of these old parts
it could be pretty pricey if they both need replacing (which I wouldn't
doubt). My alternative to just not fixing it, is to get another motor that
is newer and in good working condition for a bit more. I'm keeping my eye
out on those prices too, but have an important question to consider...
Could I use a smaller motor?

This old 80hp has powered a 15.5 ft fiberglass boat. But could a newer
motor of a smaller HP do an equal or pretty good job? Perhaps a 40hp of a
newer vintage?

Has anyone had experience changing motor sizes?

Chris