In casual observation, I am of the opinion that there were 3 versions of the L-28:1978 and earlier: Three fixed 'Greenhouse' windows on each side; Masthead rig; mast mounted over the main cabin with a compression post in the forward part of the cabin; traveler is mounted on the bridgehead (cockpit sole) just aft of the hatch.1979: 'Greenhouse' windows were replaced with 4 smaller ports on each side, the ones in the rear of the cabin would open, the others were fixed. Mast placement and traveler remained the same.1980 and later: 4 ports per side; the mast moved forward and rested on the bulkhead between the head and cabin (no compression post); traveler moved to top of cabin just forward of the sliding hatch, fractional rig.There may have some other variations in sail plan - mine is listed as a "tall rig" implying that there may have been some other arrangement.In addition to the above, there was a long list of optional equipment which could have been factory added: 3 shrouds per side rather than the standard 2; split backstay; dinette; v-berth in lieu of the standard locker forward of the head; etc.