The original factory mufflers were different from 60 to 61. Both are transverse type with 2 in/2 out, but inlets are very different: the 60 inlets go straight into the muffler, the 61 inlets have a 90 degree bend. John
That might be some good info then! Do you know if they enter and exit in the same location and if the muffler is the same size physically??? Oh yea! How the hell do you know the difference between two 45 year old mufflers
John, I don't have any references that give dimensions. The way I can tell they are different is looking at the illustrations in an old Buick parts book--the line drawings are detailed enough to pick out the differences but don't give any dimensions. You might try your local Midas shop and see if they have the data you need.
