Re: gearcase swap
The numbers won't match because the cases are different styles but they will interchange as long as they are both 20 or 25" shafts. If not, you have to change the driveshaft.
You'll have to use the shift shaft for the 150 (assuming that's the way the swap goes).
Now, the 120 is a V4 style unit with 2:1 gears. The V6 is a 1.86:1 unit. You'll need a V4 style prop to use on the 120 unit. Putting it on a V6 150 means you'll have great acceleration but it'll be a little hard on the gears, depending on how it's set up and what load it's pushing.
