I say 70cc reed valve kit.
But I am biased I have the Tomos Alukit which is the same but 1mm smaller making it a 64cc that I strapped on my Newport II and it rips pretty hard with a Homoet 4p and a bored out Bing. I run 18x36 and it takes me to 52mph. I don't have a four petal on there, yet.
I wish I would have waited a month to get the true 70cc Puch Treats kit. I wouldn't have had to modify the exhaust and it would have been a little more powerful. The hardest part is the intake. I made mine but... not everyone can do that, so it ads to the cost.
The Polini would be good too. Though, the ports are larger. I matched my Alukit and it is not too much bigger then stock and I would reckon that its comparable to the k-star. BUT the Polini is bad ass, so.....