A Number of Fun Issues!

[fixkick]

btw all engines (G) misfire at 300 RPM, its not called misfire here, this is normal. RPM is wrong, that is abnormal.
idle low can be hacking caused.

1: someone played with distributor timing
2: or played with TBI screws, say turned the stop screw wrong. on our TBI , it has bleed screw, that can be set wrong (closed clockwise max or turn fully ccw)
have a photo of your TBI? (throttle body)