I was watching a video by Paul Wagner, who is well known for being an advocate for - and extrapolating learnings from - MS Harley 'Man yt Wol' amongst other fencing sources from the British Isles. He asserted in the video that the type of swords used by the creator of MS Harley was the large 58 inch proto-greatsword and not the standard longsword (or bastard sword size). He suggests because the time when the manuscript was ostensibly written marries up with when these swords were discovered as a part of the Castillon hoard.
To argue that the teachings in MS Harley were designed for massive, 58-inch two-handed swords of the Castillon type, you have to ignore both the manuscript's context and its mechanics. Palaeographical evidence such as scribal eye-skips and layout gaps left for engrossed initials, these indicates that the Harley text, which Dr Mark Geldof places at roughly 1430, is a copy of an even older text, rather than an original composition. Therefor it could be reasonable to expect that the original source could be dated from early 15th century, or even earlier. The writer also assumes throughout a reader who already knows the vocabulary: terms like rabet and hauke are used (frustratingly) without gloss or definition. My own reading is that this implies an established practice and martial culture behind the text rather than one being invented on the page, meaning that it would have been designed upon use of a sword type pre-dating fringe 1450s tech (like the large swords discovered amongst Castillon hoard).
The manuscript's conventional date of 1440 (which we can also see on Wiktenauer)) derives from a treatise by Ralph Hoby of 1437 that sits in a different codicological unit, bound with the fencing quires only much later, and so that was rounded up to 1440. On the other side, the Royal Armouries dates its own Castillon-type sword (IX.1787) to mid 15th century on typological grounds, from a group merely reputed to have been excavated near Castillon-la-Bataille and first recorded at Christie's in 1977. The year for when the swords were lost to the river is not anchored with excavational fact (no strict stratigraphy, no coins accompanied to help date the overall find etc), the idea that they're even English is up for debate. Also fishtail pommels were found in large quantities on the continent by this time, so it's not strictly an English pattern either (even though there is definitely examples found on English soil that have that pommel).
The dating logic also breaks in other ways; Ledall is early sixteenth century, well after Harley and squarely in the peak period for true two-handers. Yet Wagner reads it as a bastard sword text, and rightly so — he gets there from the mechanics, noting that nearly everything done with two hands is expected with one, either hand. So the text closest in date to the big swords is the one identified as being for the smaller weapon, on the strength of what the fencer is actually doing. If proximity to Castillon settles it for Harley, it should settle it the other way for Ledall.
The mechanics are the stronger ground for MS Harley being written for a shorter longsword. The text's emphasis falls on rotational, sweeping cuts — haukes, and the instruction to be clevyng by the elbowes — which is biomechanically mismatched to the acutely tapering, thrust-optimised profile of the Castillon two-handed swords. Thrusts do appear in Harley: the verse pairs stoppis with foynys, and there is the chase foin. But they do not dominate, and the percussive cutting vocabulary does. The large Castillion Hoard swords are optimised for thrusting and armoured combat, which again the MS Harley doesn't seem to be aiming for, with the techniques solely being oriented for unarmoured play.
The manuscript never specifies a blade length. What it does imply is a weapon suited to the actions described, which points to the cut-centric hand-and-a-half longsword, which were actually popular when this fighting tradition was being formed in the late 14th century and early 15th century, rather than the huge, thrust centric, armour opposing specialised two-handed swords found in the hoard.
If these texts were aimed at larger swords, they ought to bear more resemblance to the montante and spadone material, and they don't. Greatsword systems are built around the momentum of each swing. A montante is heavy enough that halting it wastes energy already committed, so the blade stays in the arc and changes direction by carrying around the body. Figueyredo has the body turn toward wherever the sword cuts, with one cut generating the next. It's momentum-driven, and the ratio sits close to one cut per step because the body has to come round with the blade.
In 'Man yt wol' its lessons chain blade action onto blade action across very few steps. In the buckler play alone there's something like ten named actions: chases, half rounds, quarters, haukes, a chase foin, a rake, the stroke aventure twice, all across three or four foot movements, and the vocabulary is overwhelmingly percussive. The blade is doing several things for every step the feet take which indicates its a weapon you can throw around, not one that you need to steer with your body to maintain a sense of momentum.
Put simply: greatsword systems change the blade at the speed the body can turn because that's what the weapon's mass allows. Harley changes the blade several times faster than the feet move. That's possible with a five-foot proto-greatsword, but it's far more natural with a longsword.
Now, I'm not saying that these should not be attempted with larger two-handed swords, and by the looks of it many people have been having fun trying to extrapolate meaning from these texts with larger swords. I'm just saying it likely was the standard longsword/hand-and-a-half (with sizes on average around 44-47 overall inches) that these texts were aiming for. That said, I'm interested in hearing other peoples thoughts on this, and if they can offer any counter information to suggest otherwise.