I'm having trouble getting the 'edit' function to work, sio I'll post another reply. It's been a couple of years since I assembled my chassis, so I decided to confirm what parts I used before you go out and spend money on them. I bought the front & rear axle set for the F350 (narrow) as is being sold here:
http://www.ebay.com/itm/TAMIYA-F-350...ht_4714wt_1161
The front axle measure 166mm wide at the outside of the molded-on hexes. Then I bought his two-axle set of semi truck axles, which are 140mm wide. But, they only give you one pass-through axle, and for an 8x8 you'll need two. I bought another single rear semi truck axle, and switched the smooth rear plate on it for the pinion gear plate off the rear F350 axle. That left me only with a leftover rear F350 axle with no pinion gear plate; which I figured might come in handy if I need to replace the differential gears in one of the axles.
I bought my axles piecemeal, but if you're going to buy all of them at once, maybe he would be willing to make you up a set of only what you need, if you ask him. -Mike