I did indeed put the twin 35's on my Sierra (same as a Catalina) and it ran fine....but still stinky, loud, and fuel hungry...so I'm switching to a 4-stroke...it seems to me the important thing is not horsepower but weight...does anybody have max weight recommendation for a Catalina?
What motor are you looking at going with? I have a single 55 hp Homelite on my 19' Uniflite and you are saving about 150-200 lbs total over the old twins 35 setup and a little more than my single 100 golden meteor.
It is a dangerous misconception that you can run with almost any motor combo. To begin with, "What does the capacity plate tell you?"
That that sticker on the inside of the transom that indicates the max number of people, the max hp, and the total weight the boat will hold. If you cannot find it, call the manufacturer.
The stern of your boat will only support the weight of the motor and some extras. We had an accident near here that almost cost a little boy his life when his dad was trying to determine why the motor would not start. A friend came onboard to help and the combo of both guys and the engine began to swamp the stern. the boat sank quickly and rolled over, trapping the youngster near the steering wheel and dashboard. He was rescued successfully.
So it is not just the fact that the boat, at rest will still float, even precariously, makes it okay. There is also the question of "Is it overpowered?"