how to tune old engine without knock sensor

this engine doesn't have knock sensor

In order from cheapest to most expensive...

If you are tuning on a Dyno and budget is low then I've seen someone stand outside of the car with a stethoscope held against the engine block to listen for knock while another person is doing the tuning.

There are standalone knock detection systems available that can be added to any engine. PLEX knock monitor is the most popular. https://www.plex-tuning.com/products/plex-knock-monitor-v3/.

On the very high end there are combustion analyzers that use a special spark plug with an integral pressure sensor that can directly monitor combustion pressure.

I'm curious to hear anyone else's input. Before I had my own shop I took my car to a local tuner and told them I did not trust the knock sensor. They had someone "watch the tailpipe for signs of knock." I don't have a clue what they could have been looking for other than metal shrapnel from the engine.