smallest boat id stick a gas engine in would be a 40/80 Sprintcat.. which is 34.5" long, but you can forget handling or running in any kind of chop. For oval running in the rough, i wouldnt try running anything less then 40" long.
this is my Sprintcat (one pictured in sig) making a 77mph pass through the traps. With a boat this short, with the weight/power of gas engine.. its always on the verge of blowing off...and its hard to get enough flotation in it to keep it afloat if it blows off and drinks alot of water. Ive had it near sink a couple times..