Piston slap is very common on higher milage YB's, mine use to slap until the engine was warm.

The engine on mine itself was reliable, just not the rest of the damn thing

If it was your big ends they knock when it was cold, warm, tepid, freezing etc etc. Your compression results look good, as it's not the pressure you look at but the differential accross the cylinders. I tend to use 1 Bar as the beginnings of a problem.

Have you done a leakdown test? Was that a 'wet' comp test of a dry one?