"The image rejection is so poor on the top band of many consumer grade
radios that its really a moot point and the
only way to guess which side the injection goes is by evaluating which side
suffers the worse dial tracking..."

Right. I recently went through just this problem. Radio had been twiddled
with. The service information said nothing about whether low or high side
injection was used. I used the trial and error method to figure it out. I
looked through two different service instructions and both were silent.

The good news is that single conversion radios, with 1 rf amplifier stage,
are rarely used above 20 meters anyway, these days.

73, Colin K7FM