Tank appears to have original paint, side covers not.
Tank's original US-market, with one of the patterns Meriden supplied during '72; bike also appears to have the correct matching US-market seat - no unsightly gap between tank and seat. :bigt
Not surprised the sidepanels aren't original; they were always grp and rubbish, as is the mounting.
Risking telling you something you know already, the sidepanel badge is for a 4-speed, there's a slightly different version (big "V" under the "Trident") for a 5-speed.
About the only non-standard part not mentioned so far is the rear grabrail; as standard, it had a passenger grab loop up behind the seat, with mounting for a reflector on each side in the angle.
I notice it's missing the front fender. When/if you go looking for one, I advise a T160 or late Co-op twin one, with its completely different mounting; Meriden did fit the '73/'74 disc-brake triples and twins with a wider versions of the pre-'71 three hoops but, because the single disc twists the sliders relative to one another, the fender mountings on the hoops crack.
Someone has shortened the rear fender, originally it was maybe 10 inches longer.
Mmmm ... I'd have said that's right for a US-market '71/'72/'73 S1; there was a longer 'UK & General Export' one 'cos, particularly here in GB, we have larger rear registration/licence plates.