The ring you see on the lever is original. They bored into the lever large enough for the ring at the bottom of the extractor, then press the ring in to provide the correct I.D. for the pivot.   

Don't give the detent a second thought if it's already been wiped out.  I've made new pivot bolts three or four times and never bothered trying to recreate the detent.

I wish Stevens hadn’t used a screw slot in the pivot pins, it’s confused a lot of people trying to disassemble the action, the screw slots are often buggered up. 
Stevens published a ballistic chart in the #54 catalog (c1914).
.25-25 muzzle velocity 1551 fps with black and smokeless, 86 grain bullet.

Still amazes me that you get RL-7 to work so well.   

Just noodling around in Quickload suggests 12 grains would get you 1600 fps. with an 85 grain bullet, and at a bolt thrust that will kinder to the gun than my typical 1400 fps. loads of AA#9 in the .25-20.  Fill ratio almost 60%, which should obviate any position sensitivity.

Very valuable chart there - thanks!   

I want to assume "black and smokeless" means a typical-for-the-period duplex load, but maybe they mean that both types of powder are loaded to the same MV.

FWIW   in my experience I have found it easier to achieve acceptable accuracy with plain base bullets if velocity does not exceed by much 1500 fps.   
Of course there are several other factors involved such as rifling twist rate, bullet alloy hardness, bullet diameter in relation to barrel bore/groove diameter, bore condition and things related to the load such as powder type, burn rate, chamber pressure, primers etc.   Yes it is possible to get good accuracy substantially above 1500 fps with plain base bullets so no need to prove me wrong.   All I am saying is that for me it has been easier to get good accuracy with plain base bullets if I set 1500 fps as a limit.  Truth be told I usually find best accuracy much closer to 1300 fps when using plain base bullets.  This has been a reality for a century and a half and is why gas checks were invented so that we can still easily get good accuracy well beyond the velocity limits of plain base bullets.

Small victory - turns out that Lyman 310 muzzle resizer and seater dies for the .257 Roberts work just fine for the .25-25, mounted in a standard set of .25-20 handles.  (Had to modify the seater stem a bit to be compatible with a round nose bullet.)   

RMC has shipped my brass.  Due midweek.  Pulled some gas checked 85 grain bullets out of .25-20 stores.

I fear it'd just be the two of us - three if you left that last box of brass at RMC for another participant.