The International Cessna^® 170 Association

The original EAA STC did not specify brand. It specified "Unleaded Autofuel, 87 Min. Antiknock Index per ASTM Spec. D-439." That was found at most name-brand and off-brand stations.
BTU's are not the problem with alcohol in fuel. Corrosive effects of alcohol and absorbed water which can precipitate out of fuel which has been cooled in flight, and detriment to certain rubber components of seals and hoses are the problem with alcohol.

Interesting statement in the May 2003 issue of LPM. " fuel tanks serviced with fresh aviation fuel, as auto fuel is definitely not recommended during engine breakin - even if you use auto fuel normally."

It's in the article series about engine overhaul. They also give the Lycoming max allowable oil consumption formula: .006 X BHP X 4 / 7.4 = qt. hour. They state that the formula is good for use during any part of the life of a Lycoming engine!