I have a recipe book called Long Island Seafood Cookbook that was originally published in 1939. It has a chapter about chowder. Taking a quick look over them, it looks like all of them use salt pork. I didn't see any that used bacon. Here is the Basic Chowder, Peconic Bay. I will print the Note first.
Note: this basic chowder recipe is a good standard for all chowders. For tomato chowder add only 1 cup luke-warm water a pint of stewed tomatoes. For a milk chowder, a pint of Grade A milk. For an oyster, mussel, crab or lobster chowder-whether tomato or milk-simply substitute the desired shellfish for the clams, but always use the liquor of the shellfish; in the case of crab or lobster use clam broth and always put in some shell
BASIC CHOWDER, PECONIC BAY
2 Tablebspoon. cubed or chopped pork salt
1 Tbsp. bacon fat
1 onion, minced
1 shallot, minced
2 sprigs parsley
4 cold boiled potatoes, diced
2 Cups water in which the potatoes have been boiled
1 qt. clam broth
pinchof thyme
1/4 teaspoon freshly ground black pepper
1/2 tsp. paprika
pinch cayenne pepper
24 medium sized hard shell Clams
3 Tbsp. flour
1 pint water, lukewarm
Fry the salt pork in the bacon fat. add the onion, shallot, parsley (put through chopper with stems), and cook until the onion is golden brown. add the potatoes, the potato water, the seasoning and the lams. Heat through. Blend flour with lukewarm water and add to the chowder. Bring to a boil, simmer below boiling point 10 minutes before serving.