When we talk about “sword and buckler”, we tend to be talking about the use of a single-handed sword and a small shield. This seems to have been a reasonably common pairing of items from around the 12th to 16th centuries, with the buckler used for the dual purposes of protecting the sword hand and serving as an additional obstruction or weapon with which to cause problems for the opponent.
Prototypically, we might imagine that the sword would be of a type that is today often called an “arming sword” (a two-edged blade with a crossguard and pommel) and that the buckler would be a small round wooden shield with a centre-grip. Of course, the precise details could be quite different: the sword could really be any single-handed sword or even a messer, and potentially even a longer sword just held in one hand.
The shield could be smaller or larger, or round or square or some other shape, and it could be made from whatever material including hardened leather formed into the shape of a face. We don’t need to labour under the misconception that there is a very specific type of sword and shield that is “correct” for this discipline.
One of the interesting linguistic features of the sources glossing Liechtenauer’s Zedel and adjacent topics is that of how swords are named or described. Any given sword could just be a schwert, and it really does seem to be interchangeable whether it is a messer or sword or a falchion or whatever that shown in some illustrations.
Schwert can also be a useful term for a sword held in just one hand. The treatise by Paulus Kal seems to show a long sword or feder being used with a buckler, but it is still correctly terms “sword and buckler” because the sword is being used in just one hand.
A sword held with two hands on the hilt is typically described as a langes schwert, often translated as long sword, but it doesn’t necessarily have to be a sword or a particular (or even minimum) length. A single-handed sword with the second hand grasping the pommel might be described as being held as a langes schwert.
If the sword is being held with one hand on the hilt and one hand on the blade, it can be known as kurz schwert or halb schwert, which could be translated as short sword or half sword. Again, it doesn’t seem to matter precisely what type or size of sword it is, it would still be described as halb schwert.
All this is to say that it doesn’t really matter what type or size of either sword or buckler you decide to use. If the type of sword or buckler can be documented in the mid-15th century, then you might as well try Lignitzer’s method for using them together!