Steve Goodson's website has a lot of information on al sorts of vintage saxophones including Holton. If I were the one with this challenge, I would be using a modern mouthpiece - I always match the ''piece'' to the sax in every instance. If only all reed brands offered a ''Mix Card' as Vandoren does, with samples of each particular variety within that brand, and with different strengths. Other modern jazz makes are Otto Link ( these tend to be on the shorter side ) and Wolff Tayne. Don't 'go overboard' in shelling out for reeds, as it might turn out that this ''piece'' isn't to your liking. I suggest you might benefit from trying reeds that are better - or specifically - meant for jazz playing such as Roy Meyer, as they may be shorter overall in length compared to other more popular reeds and give a proper fit. Saxophones meant to be tuned above this would be unuseable with modern ensembles. I am thinking that this mouthpiece may have the dimensions it has because it was meant to be played with a HP ( high pitch ) saxophone that was made to be played at a basic frequency above A= 440. Have you been able to play this enough to tell if you have significant problems playing 'in tune' with this mouthpiece - or are you absolutely unable to find reeds that fit? ( Some Theo Wanne ''pieces'' are short like this, and others of this brand are longer ). The ''chimney' at the bottom is also shorter than seen on a large number of present-day mouthpieces - including some jazz mouthpieces. This isn't news to you, of course - you've already discovered that. The first thing that jumps out at me from the pictures you've provided is that the ''lay'' or 'table' where the reed sits is noticeably shorter than what we are accustomed to on say, Vandoren mouthpieces.

Unfortunately it is hard to read them, even with magnification. I've seen a few old ads for Holton saxophones reproduced on Pinterest. Holton was a big name in saxophones back in about the 1920s to '40s.

Frank holton silver alto saxophone