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The brass gearboxes you want are the dual ratio, or "5:1". I wouldn't bother with the mato gearboxes as long as I can get black steel ball bearing gearboxes, and those are only about 60 bucks (just under 50 quid). I can't say why anyone would need those specific gearboxes, but I would think around 35 to 40 quid would be a fair price.
When FDR coined the phrase "The Arsenal of Democracy", he was talking about Detroit. Proud to live in the 2nd most violent city in America!!
Yes, LeopardG, yours certainly look very, very nice, but, unless my eyes are deceiving me, your gears appear to be made of steel, and not brass. Perhaps it's a trick of the light.
"Get your facts first, and then you can distort them as much as you please"- Mark Twain.