Hi Mark,
Im really glad you posted this as it is truly an intriguing piece, and I love a good mystery!
I have been looking through some things and can offer the following as my own theory, which may be speculative, but until we hear from the experts, what I have found might serve as an operative theory.
As you have noted, the hilt is very similar to the ivory hilt example in "Swords and Hilt Weapons" (p.68) and shown as Dutch c.1660. In the same article there are a couple of other examples of these elaborate theme type hilts of Holland and North Italy of 17th century. The ivory example shown seems to have a somewhat similar lion type head but with human limbs and appears to be in the same semi-seated stance as your example. It is important to note that Ceylon was occupied by the Dutch VOC (=Vereenigde Oost Indische Compagnie) from about 1602 until taken over by British East India Co. in 1796.
The lionhead is significant to the Ceylonese (Sinhalese, sinha=lion) as their ancestry is from Prince Vijaya, and they consider themselves the 'lion people'.
This theme is seen on the well known Sinhalese sword, the kastane, and its characteristic lionhead pommel. The other features often seen are makara, semiaquatic beasts of Hindu/Buddhist mythology. The wings seen in the carving here might relate to either the garuda, or perhaps the kinnara (half man half bird).
What is most interesting is that this lionhead seems to resemble the lionhead pommels on British swords of 1770's to that of the British lionhead infantry officers sword of M1803, with the flowing mane, though closely flattened.
This does not appear to be a maneless lion.
From the 17th century there was a great deal of cross cultural diffusion in the decoration on swords, and there are Dutch swords with kastane type lionheads of 18th century, while clearly the Sinhalese craftsmen adopted themes from the European swords. Much of this diffusion related directly with the traders and diplomatic relations with the native people.
Mark, you have really carried into a most important element of research that has long been championed by Olikara and Jens, that of the importance of old coins as applied to research on weapons. Your research on these old VOC coins is excellent, and I followed your lead to the coin known as the 'dump'.
On the 1783 VOC one stuiver coin, there are two four dot rosettes in this exact configuration, and interestingly on the reverse with the date are two voluted characters which resemble perhaps Sinhalese or Tamil alphabet.
On this hilt, the two opposed figures seem temptingly similar allowing for artistic embellishment.
The adoption of simplistic symbolism from trade sword blade markings is well known and in this case, perhaps the marking from this stuiver coin, may have been presumed to imbue talismanic or amuletic power in the temporal sense by native craftsmen. The British style appearance of the lionhead may suggest this could be the work of a native carver in Ceylon about the time of the British takeover. The rosette marking may have been applied by a native craftsman on the earlier courtsword blade, and here it has been mounted on a wood carved hilt in that time.
Attached are the 1783-1793 Ceylon Dutch VOC one stuiver 'dump' coin (note four dot 'rosettes' )a VOC metal plate with similar markings.
The brown varnish on the blade may well be exactly that, as this was often applied to edged weapons in old collections.
All the best,
Jim