Our GB36 with two FL120s was built with three bladed props, both 24" in diameter, one at 18" pitch and one at 17" pitch. This was to compensate for the different final drive ratios of the BW Velvet Drive transmissions, one of which has an extra gear in it to counter-rotate the prop.
I suspect the props used on the GB42 with the same engines were similar.
A previous owner replaced the three bladed props with four bladed props at the same two pitches. On the advice of the prop shop we used, we had the pitch of both props reduced to 16." The prop shop said that, as a general rule, the pitch of a four-bladed prop is usually set one inch less than the pitch of the same diameter three-bladed prop.
This engine is "happiest" running in the 1500-1800 rpm band. However, it should not overheat when taken to WOT if the cooling system, raw water pump, coolant pump, thermostat, etc. are functioning correctly.