"which should make an appreciable difference to center of gravity?"
How, out of interest?
engine is mounted lower due to dry sump, moving center of gravity lower down .. possibly!
But then the oil tank is moved higher causing the centre of gravity to move up again
the engine is much heavier than the oil tank
Its not the sump which drives engine height on the trads - its the bell-housing and toe-board crossmember height/position. You'd only get a lower engine with a smaller/re-positioned gearbox and a smaller clutch/fly combo.
