Time to humble up and take it to a gunsmith and ask for help
The JC Higgins Model 21 is a pump shotgun, not a rifle. Reassembly should be done by a competent gunsmith.
50-150 USD
The JC Higgins 12 gauge pump action shotgun, model 20-1264 583.55 is valued at $175 in excellent condition. In fair condition, it is valued at $90.
A 1953 JC Higgins shotgun 12 gauge model 20 pump is values at about $150. It was sold by Sears Roebuck.
@ 200 USD
what is a. jc Higgins pump shot gun. model 20-12 gauge worth??
What_is_the_value_of_a_1957_JC_Higgins_12_guage_bolt_action_shotgun
Your 12 g pump shotgun was made for Sears by the High Standard Company- it was their Flite King model shotgun.
Made by Stevens, 1940's.
$125-$175.
High Standard http://www.histandard.info/PDF/Sears%20Shotguns.pdf
The manual can be downloaded here: http://www.histandard.info/manuals/sears/index.html