Will a 2006 Chevy truck engine bolt up to 1974 trans?

No, a 2006 Chevy truck engine will almost certainly *not* bolt up to a 1974 Chevy truck transmission. The engine block's bolt pattern, bellhousing pattern, and the transmission itself have changed significantly over those 32 years. Even if they were both small-block Chevys, the differences in the engine's bellhousing and the transmission's input shaft are likely to be incompatible. You would need an adapter plate, and even then it would be a very difficult and complex project, probably not cost-effective.