RPP is now owned by Athearn(Bought a couple of years ago, not long after Horizon bought Athearn). A lot of the RPP shells were designed to fit on Athearn drive trains(Logical for Athearn to buy RPP then).In fact, some of Athearn's new locos(the GP-35, GP40X, come to mind) use the old RPP molds. So the new SD38 might actually be a RPP original shell...Updated of course.
Like mentioned in prior posts, your probably have to contact Athearn anyway.
Like mentioned in prior posts, your probably have to contact Athearn anyway.