Chrysler 35 to 55

Any of you Chrysler guys know if I can replace the powerhead on my '68 35 horse a with a 55 horse powerhead of the same vintage? I know that 30 HP thru 60 HP from 1966 to 1984 all used the same size prop so I know I wouldn't need a different lower unit and prop. My question is will it fit?

I guess I should explain what I'm trying to do. I have a 21' pontoon boat with a '68 Chrysler 35 HP. The 35 just isn't quite enough motor for the boat but our home lake where the boat sees 90% of it's use is restricted to 40 hp. Now I don't want to buy a 40 just to gain 5 hp that I'm hardly going to notice, nor do I want to buy a 60-70 that I could swap whenever I go to a different lake. I happened to stumble across a complete 55 hp powerhead and carb online for next to nothing and got to thinking that if I could swap the powerhead on my outboard I could gain 20 hp but still stay "legal" on my home lake. The seller had good pics from several angles so I could see that it was identical in appearance with every bolt and mounting surfaces in the same places. The seller was not able to provide me with measurements so what I don't know is if the whole thing is slightly larger in physical size and thus won't mount up or fit under the hood, or if the HP difference is entirely displacement and carb jet size but physical dimensions are the same. Anyone know?

 

Hello
Yes it's the same! If you don't believe this just compare a power head gasket of both!