You need a gunsmith, and not WikiAnswers for this one. Sorry-
0-1000 usd
NO!!! A 12 gauge shotgun takes only 12 gauge shells. A 20 gauge shell would fall into the barrel and get stuck about half way to the muzzle. You would be in for a nasty surprise when you put a 12 gauge shell behind it and pulled the trigger!!!
-500 USD or so
Best to ask a gunsmith for help.
Based on description 100-500
1500
$100-$140.
My historical references indicate that the Browning light weight (light 12,or light 20) had the gold plated trigger from the time of there introduction.This would be 1947 for the 12 gauge model,and 1958 for the 20 gauge model.
50-5000 USD depending on specifics.
We have one in idaho. very good condition----
Assuming you have an Auto-5, anywhere from $400-$1500. Have it properly identified and evaluated.
20 gauge is larger