[xlr8or]

How about this:
Option 1: frame and body only
Option 2: The rest of the kit for option 1
Option 3: full kit unassembled (basically option 1 & 2 with a small discount for ordering it all at once)
Option 4: fully assembled roller

This way you have the same kit of parts regardless of who assembles. You already know what it takes to build your basic roller so it would primarily be just creating the template. When someone orders a car you just punch in which options they want and pull it from inventory for packaging or assembly. Keep or modify your list of current options such as fresh air kit, polishing, SS frame etc.
This way the guys in Poland can produce the same car regardless of what the order is other than the SS option. The rest can be packed for shipment or pulled for assy in Utah.

It sounds much easier than it is but with a little planning it's not too bad. I've done this with a few companies when we would go from prototype to production and the biggest chore was breaking it down to modules or areas of work. In this case it would probably be split into groups such as suspension/steering, engine bay, interior, lighting/electrical, brakes, plumbing.

An inventory/MRP system can handle this easily. You should try doing it with a product that has 18,000 parts.