A couple of long waiting customs finished?

Well they are the same class of engine because they share the same basis.

What I meant was that the round, smooth, bare boiler underneath the removable water tank looks identical to Billy's (rather disproportionate) boiler, and they just hid it using a new water tank to correct the shape. And that was the reason why people thought they made an entirely new casting for Charlie, while in reality, they did reuse Billy's tooling with an added modification.