Oversized Tubing Problem

I recently bought a Z2-80 2 Stroke engine but am having an extremely difficult time installing the thing. My bottom bar running from the forward sprocket & crank is 2.5 in x 2.5 in square. I was wondering if it'd be a better idea to buy a 49cc 4 CYCLE Motor Bicycle Engine Kit such as the one at the following website: http://www.saferwholesale.com/Compl...Engine-Kit-p/49cc 4 cycle bike engine kit.htm. I tried to attach a picture but it would not allow me from my phone. It appears that it would be easier to install this model & it looks like it would sit right on a square surface such as the bottom bar on my bike. Someone please let me know their thoughts. Thank you!