The Dick Brooks Daytona used the 305 cu. in. engine because there had already been significant development by Kieth Black and others for the Trans Am effort. I don't recall what NASCAR's max engine size was in '71, but I think the "wing car handicap" was 100 cu.in..
That motor was a direct Keith Black motor. The motor even had the same paint scheme and valve covers as the ones in Sam Posey's Challenger. I doubt that was a cooincedence.
IMHO, the #22 Dick Brook motor was just a freshened Sam Posey Challenger motor leftover from the year before.
