1988 lower on 1970 40hp?

[starcraftkid]

I was given a blown up Merc 35hp which was run without oil. The power head is trashed but the rest of the motor has very low hours. I also have a 1970 Mercury 400 40hp. The two motors look very similar, same block design, same shaft length, (20"). Is this 35hp of any use to me for parts for the earlier 40hp? A lot looks the same. Will the lower unit from the newer motor fit the older motor? The lower unit from the 35hp has the speedometer tube built in, the older motor does not.
Without having tried the swap, they appear to be the same bolt pattern and shape.