Wow, this is GREAT info, thanks! I looked for something like this and my Google skills failed me, so thanks so much for sharing.You might be interested in this Ford Body Application doc
In there you'll see the typical platform lengths that you've probably encountered talking to upfitters. (pg 15)
Note on pg 9, Percentage of Payload on Front Axle By WB/CA. Let's look at the F series crew, 84CA - 204WB. That's 7' of exposed frame infront of the rear axle and ~4' behind.
With a 12' body platform (5' rear overhang aft of axle) the chart shows 10.3% of payload (water level load) falling on the front axle. Same chassis with a 14' body platform (7' rear overhang) shows 4.4%. A 16' body is not shown (7') overhang but you can probably extrapolate the effect.
Unloading the front axle is possible with a long overhang. And tempting with all that rear real estate. As mentioned the platform mfr may not know the user's every application.
It's no small thing to put your name on a product. Caution, sticking to the "norms" may be prudent.
With RVs like the ones with the massive rear overhangs, the RV builder obviously has more control on what the finished weight distribution will be, at least until the buyer gets their hands on it...
Also, you may notice that for the same approximate wb (204-205) a reg cab chassis shows an 18' platform. That's 4' more than the crew (3' for the smaller cab and 1' more overhang. That might be only with the optional frame extension, IDK. But when you think about it, most all of those rv's with the massive overhangs are reg cabs (or equivalent). So there is something at play there.
Finally, turning diameters, that 204wb F550 shows 59'2" wall to wall (presumably that's the bare chassis without the body width or rear overhang).
For comparison, the F6/750 with similar 203wb shows 28'8" wall to wall. Significant.
It might be tempting to see a med duty 5 ton delivery truck and think, he can do it, I can do it. But know the differences.
All the above is not to dissuade you, only offered as food for thought.
In a perfect world, my intention had been to build an F-550 Crew Cab platform, 12' flatbed, and I overhang that by 2' (on a somewhere between 20-45 degree angle) to give myself a 14' floor (with a cabover). My water tanks would sit either just after the cab, or 3' after it (figuring out if I add an insulated basement or not)..
I am absolutely concerned about lifting weight off the front axle though, and I have no idea how to do the math on that. I wonder if I need to just "take Ford's recommendation" on this and reduce my living space by 2'. I'm certainly not keen to jump up to an F-650 platform.