I know this thread is as old as the hills, but here's an update:
Pocketbike "Cag" engines share the same clutch and bellhousing bolt pattern as most of the 49cc and below engines available.
Therefore, they will bolt onto all the engine drive kits on the market with 78mm clutch drums. If you remove the 3:1 chainbox, this engine isn't so wide anymore, even with the 5:1 gearbox bolted onto it.
Some pocketbike engines come with 5:1 transmissions. The trannies cost less than $30 and will bolt onto all other engines with 78mm clutch drums. Be advised that drums on this gearboxes might have different depths. The wrong drum will bottom out on the engine and lock it up. Drums with slight interference depth can be shimmed with washers on the engine bolts.
A 5:1 trans allows for excellent gear ratios, especially with 8-speed cassette and a shift kit. This allows for granny gear 1st gear and 14.32:1 overdrive/high speed gears.
I have a few pocketbike engines I've considered using. However, I've favored Tanaka 47R and the GP460 Chun Yang engines in my builds. This 46cc engine looks more like a motorcycle engine than the Tanaka. It has very good gas mileage for 5+hp, and revs past 12,000rpm if allowed to do so. The $65 Happy Time expansion chamber will bolt directly onto the CY engine with excellent power increase.
Maybe one day I'll frame-mount the pocketbike engine, using the Scooterguy mount and SBP shift kit. Then I can compare this Cag with Tanaka 47R and GP460 engines. All three of these aren't as powerful as the Morini, but the Cag and the 460 are relatively cheap and bolt right onto the available engine drive systems, like Staton, BMP, GEBE, Scooterguy, etc.