A long time ago I put a 2-1 lower unit on a Chrysler 140. It lasted for a few years then suddenly gave up the ghost and totally failed--stripped all the gears to the point where I almost could not get it apart. A number of years ago, fellow called Franz, who probably forgot more than I'll ever know, did tell me that when put on bigger engines the 2-1 did strip gears. Of course, I ignored his advice LOL.
If you compare the actual gear teeth between the 1.76 Chrysler, the 1.93 Force, and the 2-1 Chrysler you will see that the 2-1 has much smaller teeth. THUS: beam strength is weaker and the teeth cannot take as much force as the other ratios. However, on the 120 engines there is a definite performance gain over the 1.76 Chrysler lower they normally come equipped with.
Given that the 150 has so much more torque than the 3 and 4 cylinder engines, I would not expect a good service life from a 2-1 ratio lower unit.
If you have it and if you don't care about it self destructing, AND if you regularly boat in an area where losing a lower unit won't require a long tow or coast guard assistance, then by all means try it. However, I would not try to run at full throttle.
The 1.93 dual exhaust lower unit is a much better alternative AND, it has a larger Mercury style water pump. Cooling water volume MAY be a concern with the 2-1 lower unit.
BTW: Do not rebuild the original lower unit unless it is just bearings and seals. Rebuilt units are available but cost more than a whole engine. And, unless rebuilt by a professional with the correct tools it will not last anyway. Look for a good used lower unit for around 400 bucks.
