Hasn't Clem Nunn Motorcycles from W.A been running ads in VMX magazine for ages now , listing a fully rebuilt complete '76 CR125 motor including Mugen cylinder, head & manifold for $3K AUD ? Even at that price it seems like a lot of money to spend on an uncompetitive model bike .You could buy an RM125B in reasonable condition for that sort of money & go way quicker in pre '78 125 class, especially if the track was a bit rough . I see that Clem Nunn also lists a Mugen top end kit for a CR250M1 at $1500 AUD . The ad is on page 68 of VMX # 36 .