Shimano road bike conversion

Is there ever such a thing as a big enough engine? (from rc cars to Bugatti Veyron's people always want more)

I'd say you will have room to spare.
I could be wrong but I think there's a thread somewhere talking about the GT5 and maybe some others with metal shavings in the cylinders of some engines. If you get that one you may consider removing the head and cylinder before running it to be sure of any potential defects. Don't do it unless you have a torque wrench that measures in inch pounds though. And getting the piston rings back through the cylinder can be a bit tricky but certainly doable

That road bicycle and GT5 is fine. Just install than ride and later on you will know if you need more power or not. Idea is having fun discoverings things on your own. Have fun.

Go for it! Looks like a motor will slide right in that frame.

Really, that's a rigid mountain bike. That ought to do just fine, esp if the frame is steel.

Think of it as a beach cruiser with more gears.

This is a road bike http://thisoldbicycle.com/wp-content/uploads/2010/09/IMG_00201-600x450.jpg

You can motorize some but the wheels are usually bigger, the tires usually much more delicate, and the brakes probably inadequate.

I googled Konbike. I think it's a utilitarian (inexpensive, mass produced) Korean bicycle brand. Looks ok to me. They have some nice looking road frames. I can't read Korean but I like the pictures of the cold-weather overshoes and warmers. Perhaps Germany imports these bicycles regularly.
http://www.konbike.com/

the center pull cant brakes are pretty good and if you want more braking power its a easy upgrade to roadbike Vbrakes all bolts on nothing to modify. Just don't run the brake cables through the Guides. and do not hit any potholes or anything else those rims are not that strong. The Ragjoint only works on rims that have 36 spokes

yeah, look on www.niagaracycle.com for v-brake "kits". They have plenty of basic v-brakes, levers, and sets to get you done. Velocitation is a real danger on mbs if you are used to bicycles (when you are going faster than you think you are).
Mini-v's look cooler, and work for small slicks, but don't have as much power as the big old v-brakes, even the straight stick types.

http://www.niagaracycle.com/index.php?cPath=4_43_4306 v-brake stuff

$28 with cables, f and r v-brake levers and brakes, shoes, hardware. http://www.niagaracycle.com/product_info.php?products_id=431359

They got a dual v- lever too $10, if you want to use one of the regular ones for your "gas pedal"
http://www.niagaracycle.com/images/jbimages/13748sm.jpg
http://www.niagaracycle.com/product_info.php?products_id=12122
Just don't confuse yourself and nail the gas when you are trying to brake!