Is this 70 ton Flexible or not ...?

I think the only thing that I would like to add to that configuration. Would be a modular deck that would allow both a beam and deck. Or maybe a stretch deck in place of the modular deck.

 

On a trailer of this size, you absolutely want/need a modular deck - you will need to shim the deck for various weight loads. Also,it gives you flexibility to add deck inserts or swap deck types. These trailers are upwards of $300-400k and should last 10-15 years.

I would be concerned about the length of the flip neck on the big neck. To utilize a 3 axle Jeep(with axle pinned on) and 4 axle tractor you will need at least 21’-22’ for neck on the trailer and a long neck Jeep.

 

Yes the modular bogie in this case is 2,3 or 4 axles and the booster is 1 or 2 axles but the deck looks solid to the first 2 axles.
In the pics you posted I do not see room for access to the pins to change the deck to bogie connection and while I can't see it does not mean it hasn't got an unconventional pin setup. This trailer would require hinge pins to be able to shim to effectively level the bogie (and the booster) in heavy load configurations.
As @Rontonio said the jeep neck is too short for a 4 axle tractor (or a heavy front axle) to be used effectively and the neck and extension do look somewhat short for a 3 axle jeep to put enough weight on the tractor (a rough estimate from the pic is a 16 or 17 ft neck extended).

 

You know sometimes I wish I just had a heavy spec'd three axle tractor. We have a few trailer combinations just like the one above that my four axle is basically useless for.

 

The Fontaine trailers are great. I have not seen this arrangement as of yet but it looks good. We have 2 Fontaine 3 axle 50 ton units.

 

What's the difference between East and West coast setups?

 

everything

structure and functionality