The 55 is 18.5 ounces with muffler
The 65 is 22.7 ounces on my scale at home. The muffler adds alot. it alone is 5.3. I did take the fins off the muffler, weld it together and removed the baffle and long muffler screw. it is now at 3.9 ounces. the engine alone is 17.5 ounces for a total of 21.4. This is very close to the 55. if i remember correctly the 55 turns the 11x8 at 12,000 or less it is to much for it.

The 75 is very close to 25 ounces so its not a viable 55 replacement.

If you every were going to buy the 75 should just get the 95AX since is .4 ounces lighter than the 75.