John,
Never noticed an offset!
Curved to outside, flat inside. Should be self evident.
The "curve" can sometimes bind on tappet block, in which case you can file down.
Or (flame jacket on) you can also just rotate 180 degrees fit the other way round as long there is clearance.
Though I'm sure some would opine this affects pressurisation (of their anoraks)
Rusty:)