Older Receiver as power amp using tape out jacks to separate pre-amp?

If I understand your question correctly, you want to use a receiver's tape loop to separate its preamp section and amp section? The answer is NO, the preamp section still in the circuit after the tape loop, only the sources selector been separated.
sources selector > tape loop > tone control and volume control > power amp

You will still have to adjust the volume on the receiver.  You could try setting the volume at maybe 50% and then tweak it with the preamp volume.  Not the best solution.

Not possible unless the receiver has pre-out and amp-in jacks on the back panel.

Thank you all replies....much obliged