cast #2780559 = part #2780557 ('66-'71 "street" HEMI cylinder head)

are you sure those "3"s are not "8"s? (or were they still casting "street" HEMI heads in '73?)

month*day*year

G*28*8 = 7/28/68
E*29*8 = 5/29/68

H*14*7 = 8/14/67