Ivan,
Believe it not, since you truck has a 292 in already, it will be easier to replace it with a 292. For a 250 you will need to change the right motor mount, fuel in and probably the throttle linkage. Also, since you already have headers, you would probably need to modify them as the 250 is a shorter motor.
Since you want to hot rod it, make sure you have a cylinder head without the integral (cast to the head) intake manifold. If you have the separate intake GREAT!, but if not for an earlier head. You will see a significant improvement.
