I've had the recent opportunity to play three Super 20 tenors, all in excellent condition, and the two later ones just repadded or mostly repadded by a skilled repair person (metal resonators, high quality pads, lots of shellac behind them, all loose rods tightened up).
The 39x,xxx belongs to my son, and has older pads, but still plays really well. It tunes somewhat differently than the Eastlake and later ones.
The 50x,xxx Silversonic still has the underslung neck, but tunes (for me anyway) exactly like the really late one (87X,XXX Silversonic).
Also, the latter two are (for me) interchangeable in terms of sound. If I closed my eyes and someone handed me one of the horns, I couldn't
tell the difference, until I checked for the high F# key, actually maybe the slightly different neck.
The differences, aside from neck and tuning:
1) the 87X,XXX has cheaper lacquer and and plating on the keys, so it is the most worn looking of the three
2) The 87X,XXX with the "normal" (not underslung) neck has the high F#. I like this feature, some people avoid it
3) Relative to some of the earlier Super 20s (at least judging from the altos), the late ones have fully articulated pinky pads (any key will play G#)
4) All three necks are slightly different, with the 50X,XXX underslung being the longest, which slightly changes how you hold the horn.
5) Hard to know which horn had been played more, but someone played the 87X,XXX a lot. There were quite a few loose rods that needed swedging.
I would guess that it came from the factory with some issues in this area, but it still played really well on old pads. The pads got changed out because all the
closed tone holes were due for replacement, and tightening everything up required adjustment of the whole main stack, but there was no glue under the old pads to allow this.
6) I wonder if the Cleveland pads were better installed, with enough shellac, to allow adjustment?
I will probably keep the 87X,XXX and sell the 50X,XXX, but could go either way. All three horns are terrific.