One point from David Fletcher is that the Mogul has a collar around the bottom of the steam chest/saddle unit.
This is because the loco that Bachmann used as a prototype (Ward Kimballs?) had one there BUT it is NOT part of the loco when built!
This was put there because the castings (two; one each side to make up the steam chest and saddle) had in the past cracked, and as they are expensive or cannot be found (pattern makers for such castings are a 'dying breed' throughout the world, this is what has happened to the UK loco Green Arrow, where the cylinder casting is a large and complicated 'monobloc' casting, is cracked ) now the collar was put on to hold it all together.
It can be removed: it needs the front truck removed, the cylinder assembly slackened off (remove the screw underneath), and remove the thing, then re-assemble and fill in the space where the collar was with styrene card to bring it up to level.
This (especially the cab & wire) was why I painted my 4 4 0 to D&RG Colors with the boiler & cab in position!
David Fletcher's website is at http://4largescale.com/fletch/index.htm
the go to the 'Bachmann bashes'
To get the cab off (and Kevin Strong's article in GR has a lot of help), some of the tanks under the cab will have to come off as they hide the screws that hold the cab on.
There is also (from David again) a thin orange colored wire that when the cab/boiler assembly comes off is very likely to break! Beware, and bear it in mind.