Malossi 166 piston travels out of cylinder

I have a problem with the Malossi 166 cylinder kit that I have ported my engine to. When I assembled it, I was shocked to find that the Piston travels outside of the cylinder by about 5mm. I tried the cylinder on a stock VBA engine and the same thing happened. The kit number is 31 4093, and I got it when I bought my Vespa. I'm hoping that what is in the box matches the packaging. 


At the moment, I'm considering making a base gasket that is 5mm to compensate. Is this the right thing to do and where should the top of the piston sit at tdc? Any suggestions please?

Stroke is 57mm, which should match the cylinder kit.

Okay, I worked out the issue. I had been given a 139 kit off a px80. 

Note that this was given to me when I bought my Vespa, and I did not buy this from SIP.