Both the engines in the links provided by John Rist have steel liners.
To those who asked, an FP 40, Tower 40, Magnum GP 40 or LA 40 piston and liner will fit in the crankcase but all three require the head from a Tower, Magnum or FP 40 along with the head gasket.
For info, I have been running a Thunder Tiger/Magnum GP 25 with an LA 25 piston and liner for close to a decade. It is on a Ringmaster so it often only gets one outing each year and it runs just fine.