Have you read the May 1955 HRM article about modifications to the 261? Changing from the stock single barrel to two BXOVs on a McGurk manifold made a big improvement, from 2000 rpm and up. If I had a 216 Thickston to put on a 261, I would bore and counterbore the manifold to match the head and alignment rings. It will look great and run fine. If you do not want the Thickston, let me know; I have a 261 that I want to put in a classic Chevy pickup.

Hoyt