Those are indeed the Fuel Jets off the short-lived 2-stroke piston-port Duramax.
They spray the fuel into the crankcase, where it mixes with air, then travels up the transfer ports to the chamber.
I was going to run one of those engines until I got a quote for getting 8 custom expansion chambers for it.
I was going to put it in a Quadracer, until I found out that Wade had already drawn up blueprints for it and had a patent on it.
IIRC, Wade sold a member here a block without the crankholders because they are optional on a Duramax, and just make rebuilding the engine that much harder.