MD:

Timing is measured @ 2mm valve lift. (for the followers in that engine, that is roughly equivalent to .050" at the lobe)

#74 (intake) > opens 7 deg ATDC, closes 21 deg ABDC
#78 (exhaust)> opens 30 BBDC, closes 12 BTDC

The last D-jet was 1976. 1977 280E (123), & 280SE (116) were K-jet, at least in the USA. If your 280S was from a '75 or '76 the cams are the same.