'65 Evinrude 33hp lower unit questions

I became the owner of a rather clean looking 1965 33hp motor today.
(I guess I should also explain that the reason I now own it is that the last owner towed it 25 or so miles with the lower unit dragging the highway).
Thus the purpose of this post.
I've looked high and low for a good lower unit for this but no luck.
What other horse power motors use this same lower unit?
I was told by a local dealer that although the early 25hp lower will physically fit, it won't hold up?
All I've seen so far is 25hp lower units, both off early Johnson 25hp motors and a few early 60's Sea King or Gale 25hp motors.

The upper housing is good, as is the driveshaft, not much else survived. I got lucky and what remained of the lower skeg and screws all came out with little effort. Somehow the driveshaft stayed in place, but the gears, prop shaft, and bearings are gone. The water pump was all that held the driveshaft in place when I got it.

The motor is in super nice shape otherwise and runs perfect.
How far back can I go back or ahead by year to find a lower unit to fit this? What HP motors interchange?
I was told 33-40hp, but it looks like there's a change in the lower unit in the early 70's, at least in the basic casting design if not internally. The later lower unit has a smoother gear case and more angular anti-ventilation plate.
This is a manual shift, short shaft gear case.
Does anyone know what years swap and fit?
Can I convert an earlier 25hp gear case to work?

Re: '65 Evinrude 33hp lower unit questions

The early 25hp motors (1955-56) should bolt right on and will work, but you may want to look for a 1957-59 35hp Bigtwin L/U - a little heavier duty. Also a later model 28hp from the 60's will work. Must have the single water tube. 40hp is different with an outer exhaust housing, two water tubes and a thermostat.

Re: '65 Evinrude 33hp lower unit questions

I was told by a local dealer that the older 25 won't take the HP?
They use a different driveshaft and bearing that won't hold up is the way it was explained. The 33hp lower has loose roller bearings on the upper shaft, the 25hp uses tapered roller bearings.

I didn't realize that the 40hp was a different lower, I just thought they had a cover over the exhaust housing. The lower looks the same off the motor?
I've got a 1960 40hp and that lower looks like a match but I need it for my other boat, besides, that one is a long shaft.

Is the early 40hp definitely different?

Re: '65 Evinrude 33hp lower unit questions

As mentioned, the 25hp will bolt on, but as the guy mentioned, may not take the hp. The 40hp has two water tubes and a thermostat whereas the 33hp has a single water tube and no thermostat. Different lower units.

Re: '65 Evinrude 33hp lower unit questions

Not all 40s used the odd lower unit housing. 40s from the 1970s went back to the single wall mid-section, and the lower units followed suit...
Bottom line, if the lower unit came off a 35 or 40 with the silencing mid-section, then it will not bolt up to your 33.

Re: '65 Evinrude 33hp lower unit questions

I dug around an old marina today, I found a 1962 Sea King 40 that had the single tube water pump and roller bearings in the upper shaft area. I have to do a reseal on it but it looks in good condition.
I pulled about 12 lower units before I found one that matched up to the original.
I see where the lower on the 40hp motors is different, there's even a different fin or plate at the top.