What are your goals with your scooter? I understand you want solid reliability without a troublesome engine. It is important that when you decide to begin tuning your scooter, that you have some goals in mind, and that you know exactly what you want out of it.
If you are looking to get a 70cc cylinder, and still use the scooter on the street for daily use, it is probably a good idea to go with Metrakit's Handmade series of performance products. It's all made for longevity and made to be better than stock, while not pushing the envelope so far as to sacrifice reliability.
As far as the exhaust that you want -- that should be based on the cylinder that you select, etc. Anything for a Minarelli engine will fit your scooter. Some things you can specify that your engine is liquid cooled, but for the most part, everything will fit.
What kind of speeds are you looking for? It is easily possible to get somewhere in the neighborhood of 60-65 miles per hour with your scooter and still have a reliable setup. You just need to decide what you are looking for.
And how how much you are willing to spend.
The sky is the limit with the Minarelli, and 65 mph will be easy to hit, just takes $$$. I like to tell folks to just start with a pipe and get their tranny set up correctly for their weight and just live with the scooter like that for at least 6 months. I know you are ready to go faster, but it really is a good idea to get a solid feel for the scooter before swapping out lots of parts.
Keep in mind, with a kitted scooter, it will usually be more sensitive to the weather changes, i.e. carb fuel/air screw adjusting is quite common to the seasonal changes. Also roller weights will not last for several seasons, nor will the belt for that matter. So your maintenance will go UP once you put a big bore kit on. That's the price you pay to play.
Our Euro friends can confirm wether this would work or not, but I'd get me a Yasuni-R pipe if it will run ok with the OEM jug (help me out here guys). Then, when you are ready, and your wallet has cooled off from the pipe purchase, lol, you will still be able to use that same pipe with many good cylinder kits, like the one Areomyst mentioned. Also get a 19mm carb, maybe even a 21mm. Depending on rpm's a new crank might be a good investment too.
I still say get the Malossi "Multivar" Variator and Torque Drive Pulley for sure. That combo will serve you well in hilly riding situations. OEM Torque Drive pulleys have a "hump" in the grooves. This hump serves as an "overdrive", once your scooter has gotten over this hump, the belt wants to stay where is at instead of moving back into a lower "gear" position.
scootertrog