The easy way... or the hard way?

I think I have 2 options for my next build.

I can go with the regular cheapo $130 70cc engine and add a jackshaft (I'll need to buy a chain breaker and a crank puller), which requires a lot of work.

Or I can get a 90cc(???) engine as advertised here to go 75km/h with speed carb http://www.ebay.com.au/itm/A90cc-MO...ies&hash=item2c6b4bd018&_uhb=1#ht_8695wt_1155 The 90cc comes with a 36 tooth.

So which is the better option? The jackshaft option is more expensive, harder to build, and probably unreliable because of the higher number of points of possible failure.

The 90cc might end up being a dud (I heard they only really sell 48cc and 66cc which is often advertised as 48/50cc and 70/80cc.)

Any other options? I want speed for under $300 in australia!

Ok then, since I want a quality engine, I'll be buying a branded engine, and saving up for the shift kit later.

But should I get the engine from rocksolidengines? They rebuild their engines and replace studs and other parts with better parts, and say it will do 35km/h+

Or the SkyHawk GoSick:Em from mbbimports.com for about $20 which is rated for $60km/h?