I can't see any problems there.
Using the Tape input on the "H" setting should be OK (1V sensitivity to give 0.5V output, with 10V maximum headroom). You have also wired the mains cable for the 33 correctly, and I'm assuming you use a two-wire mains lead from the 33 to your 405.
I'm at a loss to understand why when you connected the screen (from pin 2 of the DIN plug) to the outer of both RCA phonos, you got no signal at all. Unless of course the plugs were not pushed fully home - but then you would have checked that. Neither does it explain why when disconnecting the shield from the L plug there was "feedback". Can you describe what the feedback sounded like? Was it a loud hum?