Howdy arknott:
Yes. In the early days of Falcon Six hot rodding Clifford's was one of very few parts sources. Clifford's started business with the logo "6=8". In the beginning Jack Clifford was it leader. It has since been taken over by Jack's son-in-law, Larry. Jack was a real participant in six cylinder performance and a promoter when sixes were considered not-worth-it.
Clifford's marketing has always suffered from exaggeration of performance gains. In the last 10 years or so it has lagged with following through with delivery and customer service.
It has also only been in the last 10 years or so that we have been blessed with passionate and knowledgeable providers of parts and information beyond Clifford's Performance.
As far as the claim of 200 hp from a 250, that is doable and has been done, and there are dyno results to prove it. I have not seen Clifford's blueprint so, no comment, but, check it out. Many knowledgeable folks here.
Adios, David