X58, X58, X58
Pretty sure MRC already did that one ...
They did, and the tooling was acquired by Con-Cor. The model still is active in their line and available direct via online order at $7.55 each. The only prototypical scheme done though is CR, although undecs are available:
1-147100 'N' 50' RIBSIDE BOX, UNDECORATED
1-147101 'N' 50' RIBSIDE BOX, CHICAGO & N.W.
1-147102 'N' 50' RIBSIDE BOX, CONRAIL
1-147103 'N' 50' RIBSIDE BOX, BURLINGTON NORTHERN
1-147104 'N' 50' RIBSIDE BOX, BORG WARNER
1-147105 'N' 50' RIBSIDE BOX, SANTA FE 'SUPER CHIEF'
1-147106 'N' 50' RIBSIDE BOX, B & O
1-147107 'N' 50' RIBSIDE BOX, ATLANTIC COAST LINE
1-147108 'N' 50' RIBSIDE BOX, UNION PACIFIC
1-147109 'N' 50' RIBSIDE BOX, WC
Crude, but passable as is and workable for kitbash-upgrading until a better version comes along.