Here are a 1973 shiney stunt 35, has the vertical ears, but note how the exhaust is faced off. A major problem with the first Fox mufflers (1972) was the as cast face on both the muffler and the exhaust; you could never get a snug fit and loosening of course occurred. I used to draw file mine flat and had no problems. Fox did this for us in 1973 and also changed his muffler to "envelope" the stack.
The other engine is a shiney 1975 stunt 35. This year Duke added the horizontal "ears". Now you could use these to hold on the muffler. They were very weak and couldn't survive much vibration or a crash. This was the last of the shiney 35s.
If you engine has no muffler mounting provisions at all, it is probably a 1963 Fox 15th anniversary special with the gold plating worn off or a SIG contest prize engine with the gold worn off. The first of the 1963 engines had gold plated head bolts and rear cover bolts.