This might help... http://www.aircraftspruce.com/catalog/pdf/L-1318G_Text.pdf
It just says that the 4270 is "Inactive"
This link will let you download the Maintenance Manual for both the 4200 and 4300 series magnetos.
You could maybe see any differences from that...
http://www.bomar.biz/download.php?list.78
The 4270 is rebuildable. I think you are thinking about the old 4000 series that were throw-away.Thanks Gil.
The big question I have is if you can get them overhauled or buy an overhaul kit for the 4270 series. I didnt think you could.