I would not feel comfortable sitting that close to the engine and that exhaust is WAY to close to your body. Let me put it this way: My exhaust runs under the foot rest of mine- about 1.5", and after a good 20-30 laps on a hot day the bottom of my boot gets pretty warm. Also hate to say it, but the engine also looks to be too far back anyway and with you sitting on the back with the engine, the front end might prove to be too light and you won't have as much control over the steering. You need some weight over the front wheels so it'll "stick". As much of a pain, if it were me I'd see about moving the engine further towards the front. That would probably solve your exhaust issue and balance out the weight more.
I dunno- anyone else want to chime in?