The P1200 plate was rated at 200 ASA - although in those days the way they rated the plate speed was a bit different. By modern standards it might be a bit quicker - but this is irrelevant, now. Over the decades they will have lost most of this speed, if they work at all. I'd try maybe 50 or 25 ISO.

Original developing time in D76 stock was 11 mins with continuous agitation. Against - largely meaningless now. The contrast of stale emulsions is usually poor, which indicates more time - but longer development means more fog, so you can't always win.

'Tropically hardened' meant the gelatin had an additive to make it a bit harder so it would stand higher developing temperatures for hotter climates where 20 degrees C wasn't practical. I think most modern emulsions can stand higher temperatures. It is of no consequence.

Let us know if you get anything.