First of all, the bomb bay looks great.
Regarding propellers: The only reference i have readily available is the Squadron In-Action book, which goes back in time aways. I do recall that the PBM started off with the Wright R-2600 engine, driving a three bladed propeller, and then the plane was re-engined with the R-2800, driving a 4 bladed propeller. In either case, the hubs in the Minicraft kit just look too small, though the propeller disc diameter looks okay and i think the shapes of the blades themselves are all right.