Truck will drive fine. Trans will work just like it did before. More motor..is a good thing. Makes it easier to drive if anything. I don't think there is much difference in the weight between the two engines so that won't be an issue. I can't think of a downside except the pure restoration thing. That is an issue for some folks. You will have to deal with the fan to radiator spacing. Not that hard. And one of the guys on this site has an adapter for the water pump to help with that, contact him.
