Wayne Calvert is still in business in Denton, TX, as far as I know. He built my 261. He used to race inline sixes in the Dallas area. I believe he calls the shop Wayne Calvert Racing Engines. I don't have the number handy, but should be in Denton directory or online.
There is another in Irving, TX. His name is Max Long. It's called Long Racing. Telephone number is 972.579.1887.