It appears that this is a High Standard Flight King (1960-63) or Sport King (1964-73). Blue Book lists the value for this gun with the High Standard name from $100 with 60% original finish up to $156 with 100%. The Sears trade name will deduct about 25% from the value.Answerwww.histandard.info
Probably in the late 1950's before High Standard made shotugns with the High Stadanrd name. Teh Flite King shotgun did evolve frm the Model 20's and 21's I don't believve there eas a Sport King brabded High Standard shotgun.
There will probably be a two letter assembly date code on this late a model 20