A brand new cam that duplicates the timing and lift of the original 261 is available from several vendors. Elgin Industries makes one that only differs from the OEM cam in the lash adjustment specification. The 261 cam was the same one that was used in the 6 cylinder Corvette in 1953 and 54. GMC cam cores are a little scarce, but I believe a few custom cam grinders still offer regrinding services. Once again, most of the available supply of GMC valve gear was used up by racers in the 1950's and 60's. What's left is E$$$$pensive!
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!