The tender of my Bachmann Niagra was too light and the cheap plastic wheel sets caused frequent derailment.So I found brass upgrade parts from Key Imports on The Bay!Solved the problem! 
Nice job, philo! [Y] And I’m sure the Lego is doing its part, too. [;)]
Tom
OK… what is the Lego brick for?
Good news on the tender fix.
[tup]
-Kevin
C’mon, Kevin! It’s a counterweight so the tender doesn’t tip forward. [:P]
Ok I used it as a wheel block alignment tool while I drilled and tapped the holes in the tender floor.
Shortly after Bachmann introduced their version of the Santa Fe Northern, I bought one, with the intention of Canadian-ising it, as the CNR owned more Northerns than any other railroad.
While I added brass details, mostly to the front end, I wasn’t trying to make it into a CNR locomotive, as I wanted it for one of my freelanced roads. I did give it a vestibule cab, though, simply cutting the sides out of sheet styrene, then, after shaving-off any three-dimensional details from the sides of the model, cemented the new sides in-place.
Once the cement had dried, I used my X-Acto to remove any portions of the original cab which showed through the windows.
The tender was a bit of a problem, though, as it had eight-wheel trucks, was an oil tender, and was abnormally long (okay for a Santa Fe Northern, but not so much for what I wanted.
One day, I was visiting a hobbyshop, (not my usual one at the time) where I saw a modern-style Tyco ACF covered hopper (lettered for Old Dutch Cleanser) that had been damaged by the sun when used as a window display. I enquired about the price, and was surprised that I could have it for nothing, as there were definitely some useful parts left on the otherwise badly-warped body.
Without going into too much detail, I cut-up the Bachmann trucks, then re-assembled portions of the sideframes into an eight wheel centipede-type bed.
I then dug-up a copy of MR from my collection, with a full page ad for a brass steam locomotive with a centipede tender - it was black & white, but nice and crisp-looking and, it was printed in HO scale! I traced its shape, then transferred it to sheet styrene, cementing them onto the re-worked sideframe. The spring detail was done using parts from Kadee draught gear boxes and some brass wire.
The Bachmann tender was then cut-up, shortened,
Nice work!you went above and beyond to build the tender that you wanted !
Painted and installed! 
That looks good, and should track a lot better than the lighter plastic version.
Wayne
Yes sir!a very worthwhile modification!
Okay, that’s creative!!
I love the ‘heft’ of the whole wheel system. It gives a good indication of how much weight the tender was actually carrying.
Nice conversion!
Dave
Thanks nice to find the correct parts so easily.