Due to the fact the only Magnetraction I own is a 736 which is packed away, I questioned the Aluminum. CW is absolutely correct that the frame/chassis side plates would be Aluminum. Depending on which issue (1950 or the later ones) would have magnets inserted into the side plate, on front driver. Couldn't find part number for early version, but later version are 2055-109 & 2055-110 (pole pieces). If the frame were steel, the whole assembly would be magnetized, and not just the drivers.
