A few years back, Leo Santucci sent an article to the 12 Port News entitled "Beating a Dead Horse". Leo didn't actually write the article, but rather it was a letter from an unidentified racer, who was relating how he had built a 261 for drag racing and went to some pretty extreme measures to get the head to breathe and the engine to stay together. I don't recall all of the details, but it was probably one of the funniest articles ever printed in the newsletter - although it wasn't meant to be humorous. The guy was running lots of displacement, a series of big cams, lightened crank, using different rods, piston height, etc. and had spent several seasons trying a variety of head tricks with lots of compression and lift. He finally gave up after reaching the conclusion that he could either make good HP, or have an engine that didn't blow up or otherwise fail after a couple of racing weekends - but not both. Please don't think I am trying to burst your bubble, but the fact is that you can only go so far with a 235/261 before you reach the limits of reliability and usability on the street. With the limited breathing of the stock head, high RPMs don't result in a lot of HP for the investment, but will certainly reduce the life of the motor.
Of course if your budget allows, a 12-port head would be the answer to a lot of these problems.
261s have had some success in circle track racing, where torque and gearing are the key factors,
but most 6-cyl round track racers these days (mostly nostalgia events) have gone to the 250 for it's higher RPM capability.
Even back in the day when there was a lot of L6's racing against flatheads, most drag racers chose the GMC engine for its sheer strength and torque. The GMC has its RPM limitations too, but breathes a whole lot better. So if you were starting with a clean sheet of paper, a GMC 270 or 302 would have a bunch more potential.
