Disregard the following if you are already aware:
A 1941 dump truck will be geared for the purpose of hauling heavy loads, at slow speeds, on 1940ish roads. Replacing the 216 with a 261 will definitely give you more torque to haul heavier loads but you may not gain much in MPH. People drive much faster today, and in my area, they always go over the speed limit. Another consideration is that big truck rear axle parts, tires and brakes by themselves can effectively clean your wallet. Some of these parts are not reproduced and finding good used parts can be very difficult. The other possibility is a frame/drivetrain swap, but any on-going discussion would have to be moved from this forum section.
