Bryce, this is truly a most exciting anomaly!! and an incredibly attractive hilt form which adds to the intrigues of the mysteries of 1788 heavy cavalry officers swords.
It seems there has never been any consensus on an actual 'pattern' for heavy cavalry officers swords of 1788,though as well known the light cavalry sabers known as '1788's were entirely unofficial...with the M1796 being the first 'regulation' patterns.
In Robson(1975, p60) noting instructions for light cavalry officers in 1788 to 'carry the same pattern as the men'.
"...the heavy cavalry officers also appear to have obeyed the instruction, at least when mounted, and to have carried the same cumbersome basket hilted pattern as the troopers".
I once had one of these 'basket' hilted types which was regarded 'loosely' as a 1788 'heavy' but unfortunately it is gone and cannot yet find photos. I do recall it had a monster of a blade (40")!! and that heavy cavalry swords tended to be quite long after 1750s (35-39" blades).
Attached is a 'horsemans' basket hilt of 1760s-70s (note horsemans ring) with blade @ 39.5". Presumably this may be the type basket hilt meant but is of course 'Scottish' form. The other type was more a branched guard.
In your example, the pommel is notable as the neo classic form of 'urn shape' which was pioneered by the Adam brothers in England c.1775 (Aylward,1945, p.63, fig.31,I) and popular on small sword hilts. British officers were inclined of course toward these stylish hilt fashions in these times.
But the complex half basket guard is more of a dilemma. I am not familiar with the Martyn book, but cannot imagine this hilt being c. 1600. While there are certain subtle resemblances to the mortuary half baskets, these were more 1630s at earliest into 1650s.
The scrolled arms on cavalry sword hilts seem to have been present on those of the Royal Horse Guards in 1788 but the hilt not quite as intricate and pommel is a gadrooned sphere. (Robson p.85)
There seems to be a bit more latitude and variation in these units with Household cavalry etc.
Returning to the pommel, which of course is not always reliable in dating hilt forms as they are obviously quite interchangeable, and often purchased from other vendors. ..
In Norman ("The Rapier and Small Sword 1460-1820, p.282, #92, #93) are two neo classic type 'vase' style pommels. In #93 it is noted that when the sides are vertically faceted the plan (shape) is polygonal. Also, that in the Boulton & Watt pattern book (small swords) there are examples similar that resemble a truncated cone from 1788. This seems to fall in line with the urn types of the Adam brothers c. 1775.
Producers of these were noted as Bland & Foster, which comes to mind as esteemed outfitter/cutlers of that period, perhaps a source for this hilt?
The rayskin grip and wire wrap is consistent with British swords of 1770s period.
With the 'honeysuckle' term, Robson notes this in describing some of the heavy cavalry sword patterns where in 1796 the 'ladder' style hilt pattern is noted and the later examples describe 'scroll' pattern where he regards the 'honeysuckle ' term more appropriate (p.157). Perhaps in searches the variation in terms might come into play.
These are just passim notes from my zero dark thirty foray into research on this fascinating hilt, which I could not stop thinking and wondering about
I hope some of it will be of some use.
Magnificent sword!
Attached: basket hilt heavy cavalry horsemans sword 1760-70s
Lionhead dragoon officers sword and troopers sword, both
'four slot' hilt design c. 1770s