i sent the engine back after flatting the head and barrel replacing studs and new nuts gaskets ect it was still the same, it drove me nuts in the end. so replaced it with a cheap china what i had in my old bike, to which i have never had any problems with from day one. i got the gt40 thing it would be a better engine and maybe run for longer but as i had experienced for myself there not so better then the china,ive had three chinas and all been ok. the only thing different form the t40 and the china was the price.
so in future i think ill stick with what i know best and leave the trouble behind me.
here is a link i found about slant heads...