a M-B.c bicycle? if that was my choice to make, i would opt for a one-off classic theme & this is what i would build:
take a classic 26" cruiser frame & put a traditional briggs & stratton 5hp minibike engine right where it belongs. rake it, triple-tree springer. cruiser bars with a >windshield<
worksman clinchers, single speed freewheel, drum brakes. big round blackwalls stuffed under full-skirt fenders. full chainguards both sides. sink a big ole cop's saddle in there somewhere. split the exhaust into two pipes, then twist them around each other in a straight line all the way back, down low, rejoin 'em for a single turndown.
a fully functional "it'll run forever" build...a tank, just an old chopped and channeled plymouth on two wheels. paint it deep purple, i think, with gray smoky flames just under the surface and barely visible light blue waves under the smoke.
wow. that was fun, i had to keep editing & editing... 8)
personally, i like the "less is more" approach. the bike in the second pic you posted, looks a bit cluttered to me. not that it's a bad bike, but it just doesn't appeal to me. i like nice smooth flowing lines and hidden wiring etc. if you are wanting to build a show bike, i like the bike in the 3rd pic best. nice lines and not a bunch of stuff bolted on it sticking out everywhere. it's all about aesthetics when it come to building something like that.
He fired it up for me at the Portland, Indiana VMBC meet; I was standing 5 feet away and the ground was vibrating from it!
On the dyno it did 71.3 M.P.H.!!!
Not bad for a Whizzer!!!
It's two vintage Whizzer 300's hooked in tandem using a Cushman truckster flex coupler, routed through an Albion three speed tranny.
I been thinking about making a little 4stroke vee twin. 60degree sounds about right. I brought home two little ryobi 25cc overhead valve weedeater motors from the scrap yard a few months ago. I will use the cylinders, heads, rods, pistons,pushrods,valves, valve covers, ignition. Make: new crankcase, crankshaft, cam, exhaust, intake manifold, flywheel. Maybe a sturmey archer 3speed hub or bendix 2speed for a transmission mounted right behind the engine. I'm starting to collect bits to use for this. My neighbor has a little foundry so I can cast the cases after making the patterns. I don't have lots of time to work on this right now...Just thinking outloud. 50cc veetwin 4stroke.
I wonder what one the 90cc chinese honda 90 copy engines would be like. I've seen for about$150 on ebay.