I did not know Wilcap made an adaptor. Let me know how it works out.
My engine is a 251 Desoto bored .030" over for 255 cubic inches. My cam was reground by Earl Edgerton 260 duration @.410 lift both intake and exhaust. I currently am running dual Carter B&B's, and a dual point distributor. Differential is 3.55/1. At 70 MPH in overdrive my engine spins as 2200 RPM's. This past June I drove my car from middle Tennessee to Tulsa, OK and back running interstate speeds with no problems. In September I drove to Charlotte, South Carolina and back once again running freeway speeds of 70+. Only problem I had was my oil pressure regulator stuck on the way to Charlotte. I have a friend with a car lift in Charlotte and drove to his house. Removed the oil pressure plunger and polished off a slight burr. Fixed the problem in all of about 1/2 hour. I have put around 10,000 miles on my engine and it is dependable.
You are lucky to have a 265 CI engine. I wish I had found one instead of the 251.