"The 500's numbers don't match any program, but #101 appears to be Harry Morrow's JBS, hiding Elvin Poe's Hodge-Podge Special.  #102 is a Cooper.

(3-14-11)   From Richard Hodges:

"I'm not convinced this is 9-10th July 1955. I can say with certainty that 101 is not the Californian JBS (which went through several hands including Harry Morrow).  I think it might be George Boskoff's Boskoff Special, as he used the 101 number, but have no other image to confirm.

102 is a "mid-period" Cooper - 1951 Mk V to 1953 Mk VII. These used almost identical bodies. I think this might be a Mk V, but haven't matched a driver yet

Car 104 is a Special. I believe it may well be a midget, probably running a 750cc Crosley engine. Several appeared, but were unsuccessful."