There is so much difference in the weight and output of the two engines that I think you will end up having to re-engineer a lot of the truck to handle the greater power/torque and the temptation to use the power to drive faster with larger loads. Axles, transmission, engine mounts (frame too?), cooling system, and brakes (maybe steering too due to weight increase).
It might be safer and simpler to start with a complete modern chassis and work to mount the older cab on it.
