Wildfire motorized bike - engine replacement?

So, I'm looking at either putting an engine on my mountain bike, or possibly buying a used motorized bike, and I found someone local who has a Wildfire motorized bike - looks like the "Whizzer" - for sale, cheap. However, the bike needs a new engine; does anyone have any experience with those, and can a different engine be dropped in? Such as the TITAN XC50S engine from ThatsDax.com?

edit - scratch that...the motor I linked to looks like it's for a completely different thing.