The only truly authentic optic I know of used on the AKSUN is the NSPU /1PN34-1PN58 (and NSP3 probably) but my understanding is that side rail AKSUN's weren't that common and were only used for special purpose reasons, not general issue.
Because of the AKSU's rear sight on the top cover not everything out there actually fits either. Kobra, PK-AS, 1P78 and 1P76 do, but PK-A, PK01-VS and the RS Regulate mount don't because they all run into the sight.
Tritium leaves you with 1P63 Obzor, 1P76 Rakurs or the 2.8x 1P78 Kashtan. I'd think they'd all be effective, even the Kashtan. I've used my PO 3.5x21P on the AKSU and again while I probably wouldn't take it into combat it does work if you don't mind the extra weight. The interesting thing is that with a Stormwerkz rail and aimpoint you can cowitness with the PO 3.5x21P. I don't care for cowitness but I discovered the system works by accident, so I'll put that out there for whatever it's worth.
For pure lightness it's hard to beat the T-1 or H-1 on the Stormwerkz rail, though I don't know if I'd drill an 86 Tula for that. (actually my shooting comrades and I go round and round on that all the time, no one has the heart to drill such a rare kit). Since a siderail is more correct and just as functional I'd probably go with Rakurs or Obzor for the AKSU but lately I've been using the Kobra again like I used to on mine.
1P78 Kashtan 2.8x
1P76 Rakurs
PK-AS
Obzor
Aimpoint and PO 3.5x21P
eta: You could also go with something really light like the Molot side rail mount or possibly KV04 and add an Aimpoint Micro that way. Rails like BP02 will also work but they are on the heavy side. RS Regulate also has the Aimpoint Micro mount in the works for the T-1 style optic, his 30mm mount on the market is very light and so should the T-1 mount.
Z