The forearm is removed by pulling downward, just grab the front of it and pull away from the barrel. There is a flat spring inside of the forearm that holds it in place. The barrel will come out when you open the action.
The pictures show that you have the diecast trigger guard, I believe that came somewhat later in manufacture. But the gun is still a early production piece.
I have the brother to that model, a Model 219 in 30-30 rifle. Savage made both as a utility type of firearm. Farmers used them for chicken coop fox's and general hunting. It was a behind the door gun or one that was kept in the barn.
The rifle has a smaller firing pin, it came in 22 Hornet, 30-30, 25-20, 32-20, and 25-35. Some models could be bought with extra barrels, rifle/shotgun combo's.
The stock set is the same as the Savage Model 94 shotgun and the Model 24 O/U. Boyd's has replacement stock sets that require only minor fitting.
I have just found a 16 gauge barrel for my 219, Snapped right into place and locked up tight as a vault.
Having a shotgun/rifle combination is nothing new, it's just the gun makers want you to think they come up with a new idea.
My 1957 Gun Digest lists the Savage 220 comming in 12ga., 16ga., 20ga., 28ga., and 410-3" . The MSRP at that time was $29.50