Well you've managed to distribute pieces of your impeller throughout the motor. You found 2 pieces, now time to look for the other 8. Check every elbow and tight spot you can. Then with the exhaust manifold hoses disconnected and the thermostat and housing off, backflush with a hose into the outlet port (the one with the hose connected to it) of the circulation pump and see what comes out of the thermostat opening.
1992 Supra Mariah - Red
PCM 351HO 285hp - PCM 1.23:1 Transmission
OJ XMP 4 Blade CNC 13x15.5RH
"People do weird things to boats" -Unknown