Did you use the flywheel off the 350? ...that flywheel is the wrong one for your motor. Surprised it even bolted up....
Not possible. The not-neutral-balanced flywheel from a one-piece rear main seal SBC won't bolt onto a BBC. Bolt circle is smaller on the SBC.
Guessing that there's an issue with the throwout bearing length, the pivot-stud length, or the linkage adjustment. But it's been so long since I've been into a clutch that I hardly recognize the parts any more.
OTOH, if this is a hydraulic clutch, I've had problems getting the system bled properly. I ended up pounding the clutch pedal from foot-off to "on the carpet" about two hundred times, as fast as I could pump. That is, pump 20 or 30 or 50 times, hold the pedal down at the end. Let the bubbles rise to the top. Release the clutch so the bubbles get pushed into the reservoir. Repeat. Make sure the reservoir doesn't run low.
No amount of bleeding at the bleeder screw was helping.