I think either mounting arrangement you show would work. What Eric pointed out is true, and would seem to argue against your second drawing; practically speaking, though, the expansion of the middle cone will be very small, and will be mitigated by the "heat sink" nature of the mount spades, which will tend to cool the cone by conduction and re-radiation (or conduction into the supporting device). Shown here is the "vise grab" rails I provided on the Lady Guinevere (they are parallel, NOT diverging aftward with the cone!!!). Your first drawing is a better plan, though, since it is longer for greater stability and provides a "sliding fit" at the rear end.
Theoretically, the no. 1 best place for a rigid thrust-bearing mount would be at the outer edge of the front dome. A close second is the center point of the dome, using the spark plug as the mounting bolt (the Steve Bukowsky mount). Of course, either way, you still need to provide lateral stability at the rear (the keeperfrumfloppen mount ;-).
That will work, IF you cut them really short. If you let too much of the transverse part of the ell remain, the direction of the intake air will be too much "inward" and not enough "forward" - you want to make sure the explosion center is developed as close up against the front dome as possible. If it's aft of that, the lengths of the design will be wrong in terms of the actual acoustic behaviour, i.e. the pressure antinode will not be at the dome end of the pipe.For the intakes I am going to use 90 ells cut to fit as opposed to the angled units and keep the C/L length the same ...
Don't try to get the centerline length "around the bend" of the ell. You would need to do that if the ell had a long leg going into the chamber, but not if it is tightly trimmed as just suggested. Instead, get the design length from the rearmost inside edge of the cut face of the ell back to the flare edge, treating it as a straight pipe. That's how I lay out the dimensions on all my recent drawings (illustrated also in many different intake geometries on the "FWE Evolution" drawing published a few weeks ago).
Knowing what to do with that "transition" can be tricky, especially if you don't want to custom build it. Just keep in mind that in the FWE design you ideally want the fuel/air mix to enter, flow forward and come to rest with a slow splash against the front dome, just as it explodes. Getting that detail right was the total problem we had with our attempts at a "front loading" intake. I think my own best designs for the intake pipe were on the Smooth Lady and Sveldt Lady variations - both quasi-transitionless designs (almost like Thermojet intakes), with the "transition" reduced to a little turned down lip at the top front of the intake pipe.