Using the flanged bearings
I found that about .7 or so gap needed to be filled in on each side. While finding a .7mm washer is rather hard...you can get some Tamiya 53585 shims
to make up the gap (they are cheaper from just about anywhere other than TamiyaUSA). They come 10 each of .1, .2, and .3mm, and are small enough that they wont hit the outer races of the bearings. Here's a pic of my mod, I used a .5mm washer in there along with the shims, but just a pile of shims should work the same.