TOPIC: Dorsett Catalina- sizing kicker/motor HP?

I have a 1958 Dorsett Monterey (early Catalina, pretty similar from what I can tell) and at some point i'll be upgrading the ancient 60HP Mercury it came with. I live where outboards are expensive on Craigslist and it's going to take me a while to get the used motor I want- which means I don't know what size motor I will eventually have. I'm thinking it'll also be a 60, hopefully 4-stroke.

In the meantime I want to put a kicker on it (it already has a kicker bracket) because I don't trust the old Merc and because things like to break and I want to be able to self-rescue.

How do I calculate motor sizing and weight for a future motor plus a kicker? I know 4-strokes are heavier (I'll probably get something that's 20 years old, or a 2-stroke around the same age with fuel injection, because older 2-strokes are banned on some of the lakes near me).

how do I pick shaft length for the kicker? it's mounted in the usual place off to the side on one of those brackets on a hinge that swings down. Do I measure from the bracket down to the bottom of the keel on the transom like if I were picking a normal outboard?

How about horsepower and weight?

Thank you all!