I heard back from the factory on two items:

1) 915 weight and balance: Keeping the parachute in the new forward location and moving the rear seat back to it's original position (simply by not installing some parts that move them forward) will be OK with the 915 (or in my mind the 914 with the fuel injection add-on).  So, that's the plan.  With this I can make the 914/915 decision later.

2) The VS fitting issue:  They said my measurements are within range and the way they put it in at the factory is to use plastic guides on either side of the VS as you push it in from the rear.  It will likely push out the sides a bit, but that is expected.  Since Peter and Gordon are well ahead of me, they'll be testing this out before I do, so I'll be anxious to see how it goes.