Bingo, have to get lucky some times, found the barrell!
Went past a wrecker today and thought I'd drop in for a look, had a rumage about on the shelves and out comes a likely looking 248cc barrell. Hmmm, big hole through it me thinks as I scurried off home with it for $20.
Just pushed a 305cc ring into it and it looks perfect.
So hopefully I might get away with only a hone.
So....... if anyone know the where abouts of a cylinder head assembly my life will be complete.