Nice find sanjoh!
I haven't heard of too many engine transplants in the 200s. The Warrior engine would make your bike into a slightly higher performance BW350 with an extra gear.
I'd like to know if the Warrior transmission could be swapped into a BW350 bottom end, as that extra gear would come in handy sometimes.
The angle between the cylinder and case halves is different between the Warrior and BW engines and that might complicate the installation. However, the mounts seem to be very accommodating for a number of builders.
As far as I know, DC Plastics and occaissionally ebay, are the only sources of plastics. At least you have you side panels and that puts you miles ahead in the game.
Here's another shot of Cliffas Pastrana charging hard above the tree line in the Talkeetnas: