My first boat was a '93 Rinker 206 with a 4.3LX/Alpha. Great little boat and would go a long ways on a tank of gas (40 gallon if memory serves). My family's first boat was a 1973 Glastron 16 1/2' open bow tri-hull with a 140 HP Merc (motor might have been a couple years older than the boat). No good place to sit in that boat - in the front your kidneys would bleed and in the rear jump seats you thought at any moment that screaming Merc would ventilate itself and put a rod through your ear. No built-in gas tank either. We carried 3, 6 gallon portable metal tanks that fit back by the battery under a vinyl curtain. I was the designated "bulb boy". Every time we ran out a tank I had to switch to a new one and prime the line by squeezing that bulb that always seemed to be leaking fuel. Good times, good times....
Speaking of Mark Twains, which the Illinois river was full of back in the 70's, does anyone remember Sea Sprite? There were a bunch of them running around as well.