Fastwin 4 Bolt Lower vs. 5 Bolt Lower.....

[SeaKaye12]

Hi.

I have a 1955 Fastwin 15 HP (53014)
The lower half of the lower unit is buggered and needs to be replaced. I found a lower unit from a 1953 Fastwin 15. It differs in that the older one has 4 bolts to the exhaust housing and the newer one (mine) has 5.

My question though is....is the lower half the same?

I have parts diagrams for both motors but they treat the two halves as a unit and I haven't had any luck finding the answer anywhere.

Thanks, Chuck