Many have replaced the Amal Concentrics with modern carbs, but I fitted new Concentrics to my old bikes when I rerstored them and they run great.
Both have chrome slides which prevents (or at least greatly retards) the wear between slide and body that was so common on Amals and led to poor running.
I had the carb for the BSA Victor sleeved at first, but the bike still ran poorly. I bit the bullet and bought a new Amal and the difference was like night and day.
The new Amals with hardened slides, replaceable low speed jets, stay-up floats & viton-tipped needles ARE modern carbs. They just happen to be based on an old body design that doesn't need to be changed to "work better".