Chuck, if memory serves, it is a Bisson. The exhaust pipes are slightly off-set from the center line. I fit a new cowl after the engine swap. The Twister replaced an old baffle piston K&B .61 that I couldn't get to hold a low end needle adjustment. After the swap, I found all the old engine needed was a new 15 cent "O" ring. I'd post a pic of the Cub, but it is so beat up I'd get booed off this thread. I have an idle .70 FS I could put in the Cub, but the K&B runs so sweet, I hate to mess with it.