Nope, that is it. The straight cocking tube fits tight into the front sight post, and the tapered cocking tube leaves room for the barrel and front sight post to "free-float" to enhance accuracy. Any G3 made by HK marked G3FS are either a G3A3 or a G3A4 depending on stock configuration. Any G3A2 with the fresichwinger mod and FS restamp will therefore be a G3A3/A4.
And if you really are that interested in all kinds of detail differences, go buy "The full circle", lots of info there.
Like that the steel handguard G3 is really early HK-made CETME prototypes/T&E models for the german government, IIRC called CETME DM3 or similar meaning CETME Deutsche Modell 3 or german model 3 in english.
And again, go buy the full circle....
mg42 over and out.