"The Pacific Grand Prix entry list for October 1964 includes a #50 Shelby American entry in the pro race for Ken Miles with engine size at 6500 cc (that’d be a 390 as at Sebring or Nassau, right?).  However, I don’t remember if it qualified and ran.  I’ll have to consult my periodical sources. 

I do remember watching Miles in a 289 #50 in light metallic blue at the 1964 USRRC Manufacturer’s race chase the uncatchable Ed Leslie in his black #98 (red gothic font numbers) OA winner.  So pending my finding more info about the 10-64 entry’s livery, I imagine that the Laws photo has to be from May 1964."