I was looking at your pics and haven't seen a lower unit like that before. Is that a prop cover or a jet unit? What brand?

Hello! What you're looking at is a "Pump Jet". It was commissioned by the USMC in the 1990's. They're made by ACT [Applied Combustion Technology] out of Orlando, FL. Check out this link here: https://actorlando.com/pump-jet-propulsion.htm