Jordan, out of these two engines I would go with the Chevy. It would be a lot less work and from my experience the International is a real dog.
Those old Chevys are super reliable and I see it has the HEI distributor which is bullet proof. I have a bell housing around here I think that will fit that engine. A hydraulic clutch would eliminate the reverse fork problem. Clutches and flywheels are the same for many years. The engine has side motor mounts but that's just a matter of making some brackets. This engine would certainly work well if this truck is to be a CC7 driver .
Barry