While the rear end itself is essentially the same, the mountings are different. They can be modified, but it requires some fairly precise cutting and fitting, and welding of adequate strength. Note that most cars with OD had a 4.30 ratio, versus the 4.10 of the straight 4 speeds, which includes PVs with the B18. (B16s had 4.56)

It should have an M41 with D type OD, though, as someone else mentioned below, check to be sure it's still there.

If the car is cheap enough, it would be worth buying as a money maker. Early P1800 trim parts are pretty scarce these days. What kind of shape are the cowhorn bumpers in?