Prototype drawings of BN's Trinity 4750 three-bay covered hopper were published in BNSF Railway Freight Cars Volume One by Robert C. DelGrosso (Great Northern Pacific Publications, 2004).
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Athearn N ACF 2970 Center Flow
At 1 ounce, the two-bay covered hopper is .1 ounce too heavy per National Model Railroad Association ... ACF Leasing; ...