Pat, we need pictures of your engine to discuss it usefully. It was made on 4 April 1977. Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6jmvGVJ1DajI.pdf

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/lrvvA-wU7eL7hAxB91ObQ.pdf

You routinely remove the cowl, fuel tank and carburetor whenever you need working room on that engine.

Briggs used several mufflers on that model, and most others. Let's see which one you have, then we can talk about it.