I just bought a K&B .65 Sportster on ebay without a muffler. I’m currently looking at a K&B muffler that says:

(directly from ebay)
“New, perfect condition, K&B .61 muffler. Aluminum construction, expansion-type design for maximum muffling. New, never used or bolted on an engine. Includes pressure tap. Fits K&B .61 & .40 and H&B .61 & .40 engines, also may fit others. This item guaranteed as described!
This muffler is super light weight! It weighs only 3.2 onces, this is 25% lighter than the same size HB muffler.
This muffler may also fit the following engines: HP .61 & .40, Webra .61, Tower .46, some SuperTigre .60's. This list is not complete just what I can find out from asking other RC users. The rectangle exhaust opening measured at 5/16 inch X 1 3/16 inches. The distance between the mounting holes (from center of each hole) is 1 1/2 inches. “


I don't have the engine yet, so I can't measure. Would this work on the .65 Sportster? Thanks for any help.
Max