I prefer to run the earlier center water outlet type engines in 39 and older trucks. The 8BA is a great engine, the best flathead V8 series in terms of use, but fitting one into the earlier vehicles is a bit of a juggling act. The center water outlet types just bolt in and use a stock fan. With an 8BA you're probably going to end up with an electric fan.
JWL did careful testing on a dyno (specifics in his very good book
Flathead Facts) and determined on an 8BA there is no need to swap out the factory distributor unless you do either one of these two things:
1 - run a non-factory camshaft that messes with the vacuum signal to the carburetor
2 - run a non-factory carburetor that lacks the specific vacuum signal for the distributor (it is NOT manifold vacuum).