Ive read its the same tank as in the Matrix, if that helps. Isnt it listed in the manual for the Magnum? Might be worth trying to download either manual and see.

Or... contact the guy on this link through ebay and ask about the $0.95 tank listed way down the page... http://okvrv.org/125cc.html

No idea on the platic top plate though. But I think I know what youre planning on doing - hmmm, nice.