Does it have the 305 engine? I am thinking that will be a tight fit in the 42 engine compartment and might require moving the steering box, etc.
The front end on the caprice is way different from the 42. The suspension is way better and I doubt you can use the brakes, although, some one does sell a disc brake adapter kit for some drum brake 1/2 ton trucks. But I think its mostly from 48-59 trucks.
Is your truck a half ton?