'61 S/Rocket HHC marking - or not

[Cyclops]

My '61 S/R is stamped DA10R **** but no HC or HHC. I believe it's an abbreviation for High Compression and do remember my '63 reg. S/R back in the day having those marks stamped on the c/case.
Also, whilst having the cyl. head off recently for repairs i noted the pistons were flat top, not raised or domed. Is this likely to be standard or is it possible that a previous owner has fitted lower compression items.
Any info gratefully received.

[JulianS]

The SR cases were usually stamped HC for high comp or HHC for high comp and high lift cam.

Flat top pistons would normally be low compression, probably a number on the top if BSA or old Hepolite  which would identify them.