Load data, if I understand correctly, is determined by bullet weight as well as by bearing surface: In other words, a bullet with less bearing surface may tolerate a slightly higher powder charge than the same weight bullet of a different nose configuration because less of the bullet will be in contact with the lands and grooves during the trip down the barrel.

Now, having said that, the load you are using is so slow in the pressure band you will not have any problem substituting the RN for the wadcutter. Your RN will have less bearing surface, so if what I understand is correct, your load SHOULD be even lower in pressure than what the Lyman book states.

You can also use the 158-grain data and tailor a load specifically for your bullet. But I believe the 150 load data will work well for you.

FWIW, I have been casting and loading since 1980; I don't know much yet, but I have learned that there is a lot of "room" in handloading if you are careful, use your noggin, and go slowly.

Good Luck!