There is the infamous Dragnfly.Its a mini bike frame pusher.The place in CA that used to make em doesnt do it anymore,not sure what happened.Anyway using a minibike frame pusher has at least one positive aspect.That is you can carry cargo on the top level of the frame.
Back in 2002 they took several Dragnfly's and ran a charity event that started in Mexico and went all the way to Canada.They had many pics of the trip on their website.It was amazing.I don't think their site is up any longer.
If I remember correctly the one thing that's important for balance of the mini bike frame pusher(if using the larger engines-weight) is on most of these frames you either need to widen it some or run a jackshaft set-up.Reason is when you place the engine on the mounting plate holes,it's not often balanced causing the pusher to pull your bike to one side.Not all frames but still a great many.The widening of the frame is so you have room enough to run your chain without hitting or even going past your frame,after moving your engine for balance.Widen or jackshaft.