Just cut this off of a 1978 is this from the factory?

 

D8 means 78 and its has a script ford badge on it.
Looks like the original to me.

maybe the 10 77 means made in October 1977?

 

Anyone else running a 39 year old muffler?

 

Running a 44 year old muffler on my rig, thing is dead quiet

 

Pulled the original muffler off my 78 Bronco a couple of years ago only because I decided to go with some headers! The thing was about 98% original!

 

My '78 bronco had the original muffler, and a tailpipe with some sort of spark arrester in it. Muffler was cracked in a few spots and the spark arrester created massive restriction. Would not exceed 55 mph under any circumstance with that setup. Standard tailpipe and a flowmaster made a big difference.