The big worry with a whitemetal chassis is that the thing won't be flat. Castings have a tendency to subtly change shape as they cool and while that might not be an issue with the pretty bits, where accuracy matters, this is a bad thing.
You might wonder why if I'm so worried, I didn't replace the lump. Truth is, while there are only 4 wheels, I'd need to hang the cylinders and valve gear of it. More to the point, the body has to sit on top and pivot. Since the arrangement shown in the exploded drawing looks pretty promising (read, quite like the setup seen in old RTR) I don't fancy trying to re-engineer this.
Anyway, a quick check shows the chassis is flat so far. If it need a tweak, at least the metal is soft enough for this to be reasonably easy.
And in case you are wondering, the metal disk is from a computer hard drive. It's more robust than glass and flatter. I'm proper hard finescale like that.