Not a slant. 1947 boat Engine

First thing to check would be the points in the distributor. My dad had a 58 flat head and points were a problem, but that thing would idle with a glass of water on it and not spill a drop. After driving a flat head and then driving an OHV 6 it was day and night with the better pickup in the OHV engine. Surprised they stayed so long with the flathead, especially after they came out with the Hemi in 51.