Help me repurpose Echo Matic Tape delay circuit to general Feedback send/return

So again i was more smartass then smart and finished the echo matic pcb wich i had gathering dust bc the lack of a tape recorder.

To incorporate a send/return feedback mix to my filterbank into spring tank or chip delay i populated the pcb just now only to realize there isnt an actual Signal INput on this circuit.

Like this i obviously cant have it accept a signal, send/return mix it with effect and have it at the output. Obviously because it was meant for the tape device to recieve the input.

My head doesnt quite get around how i should manage to repurpose it in my intended way if at all possible. If not, is there a simple diy feedback mixer kit idealy working with a spring tank?

I wanted to create a feedback loop for the filter bank first of all

https://easyeda.com/MattDGTL/echo-matic-new