Webley & Scott 12ga Single 32" Barrel -Value & Safety

I purchased this shotgun used about 40 years ago and have not used it in probably 35 years! The barrel is marked 3" with a 12 inside a diamond and 3 1/2 Tons per square inch. Is it safe to shoot today's 3" magnums in this gun and what might be a realistic value for this item. Any help will be appreciated.