Chris,
Don't have a good source for that either, sorry ...
But the additions/changes with code 49/1 (or 491) changed over the years; will say more changes were introduced the younger the SLs are. A 1971 280 has much more changes associated with 49/1 than a 1964 230...
(the latter only having sealed beam headlight units, English instruments, omission of the horizontal polished aluminum "chrome" stip under the rear number plate... ).
So, it's heavily depending on your "model" year.
Achim