Sorry your question has gone unanswered these past few days VickLeee but let me take a shot at it........
Your idea suspending the top for trial fitting on another profile is very sound----it would greatly simply not only that trail but making templates for re-contouring that top to another van roof. I'm completely guessing most American vans would have a similar profile so modifications to the existing might be minor.
First step would be putting your idea into motion and inviting other van owners to temporarily park in your fitting room.
Once you know what differences you'll encounter how best to proceed should pretty much lay itself out all on its own.
Please let us know how this goes----BTW we love
photos of your progress beginning to end here!