I recently bought a BLP billet duel pattern base plate for my 1000 cfm 4150 carb. It is a high quality product. In comparison to the Holley billet plate I am replacing it matches transfer slot location.
I'm going to run this carb on a trick flow 270 head / max wedge size intake with a 4500 flange. It is not assembled yet so i can't comment on how it runs yet but so far so good.