The K-Line die cast hoppers are very close to the old Lionel cars. To really make them look good one needs the 700- series bolster castings. I was able to buy a couple pair from a really nice guy in New York, but generally had to make them from brass.
I converted some for others, and simply made brass shims, but I remember that as being a task for the end mill. Too bad nobody has yet resurrected the 700 freight cars exactly. It would be so easy, considering how close they have come.