The stroker kit comes with a crank (a 4G18 crank.. apparently it's derived from the one used in Waja 1.6), conrod bearings (undersized to compensate for longer stroke), pistons (slightly oversized), and probably also a flywheel (since the 1.6 engines use 6-bolt flywheels but 4G13 and 4G15 use 5-bolt flywheels).
Basically, it's to change a 4G15 with 75.5mm bore x 82mm stroke into an engine with something like 76mm bore x 87mm stroke. The bearings will need to be undersized units so that the additional stroke will not cause the pistons to intrude too much into the upper cylinder area, whereby they might strike the valves at higher RPMs (when the valves start to "float").
Why not e-mail Powerzone and ask them? Sirazul always finds time to answer e-mails.