yeah, i'll shoot my buddy an email, he's going into the 'local' moped shop (yes, the town he lives in has a moped shop, that he can like, ride his moped to, how rad is that?!) this week for me to check on some prices and find out if they can get some parts. i'll add 'austia rings for sachs 65 cc kit' to the list. What size are the rings, you should measure it and try to find a cross refrence, i'm sure something else out there uses the same rings.
So does the 504 use the short 'A' stroke or the long 'D' stroke? If i were going to mod a cylinder/kit to fit on a mismatched engine, i certainly wouldnt do it with a file. that would definitely be a 'lathe' job. I would probably put some modelling clay/silly putty in the D cylinder spark plug hole, put the cylinder on, crank it around, pull out the clay and measure the thickness at the thinnest part. Add, say, half a mm, and have a machinist remove it from the bottom of the jug. If you dont know a machinist, send it up here and i'll make quick work of it. CHEAP!