The 4150 manifold is easy to convert to the 4500.

1) screw aluminum bolts into the bolt holes
2) cut them off flush
3) drill and tap the new 4500 pattern
4) open up the plenum to clear the 4500

I am not suggesting that the 4150 manifolds are better than the 4500 manifolds. Just a heads up on how easy it is to convert one. One of my favorite manifolds was a Holley Street Dominator that I converted that way. Worked real good and fit under the hood.