Hello, Gerry from the US.

You bring up an interesting sax that I hadn't seen before. Just doing a little quick research, your model in playable condition and reasonable cosmetics fetches still a good cost, example, from MKE Music Supply in Grafton, WI US, $1,895 US with free shipping in US:

https://reverb.com/item/47103151-1938-buescher-aristocrat-series-i-slant-signature-art-deco-professional-alto-sax

Some more information is available on:
https://jazzfuel.com/guide-to-buescher-saxophones/

In the series, they also had a C melody sax in the series. Not done much now, but back then manufacturers were making these, for people who wanted to read off, say, a piano score, accompanied by the piano, without transposing.

I could not find any indication that it was anything other than an Eb instrument. In playing it, have you found what key it might be in? It may be possible that mouthpiece acoustic length is different with modern mouthpieces (I only speculate because I don't know). Also on some saxes, I've had to insert the mouthpiece with the neck cork inserted deeply all the way with hardly any cork showing.

But since you have the original accessories including the mouthpieces, I'd just play it with those, or have someone who knows sax play it. Then by comparison with a keyboard or piano, could determine the key.

But, looks like you have a keeper especially if someone in the family plays sax, with repair / checkout or overhaul by a competent technician.

(Photo from Reverb listing)