IF you are very careful and choose a frame with not only enough clearance but is also the right shape - yes, it's a very simple bolt-on. The easiest bikes are those with the traditional triangle shape, this is getting harder to find nowadays what with oversized D-tubes and unusual bends. Grip shifts are also common, you can get around that with a thumb throttle tho. Pedal crank clearance can be a concern, needing about 4 1/4" between them to clear the motor - most fit fine.
All in all it's only the rear "clamshell" sprocket mount that is tedious in any way, you can skip that headache by pickin' up the Manic Mechanic Sprocket adapter;
Although the supplied sprocket and mount is ...usable and many do - as a motorcycle mechanic you'd prolly be horrified by it heh
Yet with a bit of patience and creativity (and a lot of cussin') you can motorize just about any bike with enough room to fit the motor. If you decide to go cruiser style - those bikes have SO much room you can even use an engine mount platform (also available frm the dealers here). I of course went with everythin' I just warned against lol my mountain bike was a tricky build, at least it didn't have grip shifters. I also commute with mine on a daily basis, rain or shine - I've had no problems
The 'Grubee Starfire' is the kit that generally includes the better components and here is list of the businesses I've had good dealings with (in no particular order);
ThatsDax: bicycle engine kit, bike engine, bicycle engine, bicycle motor
SpookyTooth: Spooky Tooth Cycles - Motorized Bicycles: Gas Powered and Electric Bikes - Home
BikeBerry: Bicycle Engine Kit - Covert any Bicycle to a Motorised Moped. 150 MPG!! Wholesale Beach Cruisers, Chopper, Mountain, Road, Tandem and BMX Freestyle Bicycles. - BikeBerry.com
Sick Bike Parts: Sick Bike Parts LLC - Performance Parts for Your Motorized Bicycle
Manic Mechanic: MANIC Mechanic Parts.htm
Most of those folks are often on this forum too - a handy thing no doubt
Good luck - I'm lookin' forward to seein' yer build!