No direct experience, but some people I've spoken with comment that it gives a somewhat lumpy idle, and low manifold vacuum at idle. "Valve open" duration (discounting clearance ramps at both ends of the lobe) of anything over the mid-260 degree level tend to kill low end torque and produce a choppy idle. That's true, no matter what engine we're discussing. The Elgin clone of the 261 cam (E-323S, I believe) lists a total duration of "300 degrees"- - - -but they include the total deviation from the base circle of the lobe, including clearance ramps on both ends, when the valve isn't actually open. The actual valve open time is in the high 250s or low 260s, IIRC. That's the cam we put into John's 261, and I degreed it during that engine buildup session. He's very pleased with it. Elgin isn't producing that cam at the moment, but I've got a brand new one that I'm planning to send to Schneider Cams so they can make a master cam from it. Then they can grind as many of them as they want as long as the have a good core to regrind- - - -solid or hydraulic cores don't make any difference- - - -the finished product will use solid lifters.

Boring a 261 to 3 7/8" would result in some paper thin cylinder walls, in my decidedly biased opinion!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!