My new small block Mopar (not an A body)

My Folks had one of the big Southwinds with a 440 in it. A year of so after my Dad died in 84, my Mother decided to go on the road and bought a Dodge motorhome (based on the van). I drove it a few times and thought the 318 in it was underpowered for the size of the rig. Needed at least a 360, or better yet a big block.