Re: chrysler lower unit compatibilty
That is the old 2 piece lower unit with a splined propshaft and thrust pin prop. It was used in two styles up to 1977 or 78. You can use almost any lower unit from any 3 or 4 cylinder engine up to that year. The earlier lower unit was a little less streamlined. While the casting looks different, it will still bolt up to your midleg. in those years, the only 2 to 1 ratio lower unit was the 90 horsepower engine. This ratio will wake up your engine and is good for a couple of MPH more with a prop pitch change--go up 2 pitches.
Later 2 piece lowers like yours are three bolt, meaning that three studs pass up from the gearcase and secure it to the upper portion of the unit. Earlier lowers were 2 bolt. Obviously less strong but still well able to handle anything your engine can deliver.
Props for the 2 piece are becoming difficult to find and no longer can be re-hubbed. They do come up occasionally on ebay BUT tend to be expensive.
If you want to put in a couple of hours over the winter, you can change the midleg and lower unit to the newer one piece. Everything else will remain the same. This is worth 3 MPH more and you have a much better selection of props.
The two piece lower is NOT swappable with the one piece lower. The midleg and driveshaft is one inch longer on the two piece.