Definitely looks like a test mule now. If the price point on these can be kept down with a good quality Ild wager they would sell.
From the inside you can see that they're factory uppers with a new outer skin and a slider window:
They could be a DIY kit, but bonding the fiberglass outer shell to the plastic inner shell requires a specific procedure and a special gun - it's a two-part adhesive that comes in dual tubes and requires a dual-tube gun, something all auto body shops would have but few DIY-ers (except me) would have.
Any chance you are gonna try and do the lower half in fiberglass for a complete set?