Emma and I did the same trip in Patches which David and Ashleigh did, except we went up to Glacier. After getting to know David's rig, I have to say that the pop top is the way to go. Patches' high roof is not bad, but I'd take a pop top over my 12" of non-movable roof any time.
I've thought about putting a Westfalia top on Patches, but living 14,000 miles away from it has put a real damper on projects for now.....
I say cut the top James. If you think you can mate it up so it does not leak, I reckon that would be the way to go. You've already got that great camper interior; what a combo that would be.
Josh