OK, here's my notes on working on this trigger. Recommend a good gunsmithing screwdriver bit set for any work on a gun. Also refer to pics in post #8 above. I will edit this as needed.
Tools needed: hammer, bench block (e.g. a flat piece of wood, like a small section of a 2x4 with a hole drilled into it); small punch; long thin needle-nose pliers; something to tie the trigger back, like a twist-tie, for reassembly ease.
1. Pull the action--one flathead screw.
2. Pull the Trigger group (TG)--two flathead screws.
2a. Might as well polish up the feed ramp while you're in here. I use wet/dry sandpaper, 400 grit, then 1000, then 1500 for all my polishing jobs. This one was already nicely polished, so I just took a few seconds with the 1500 grit to make sure.
3. Knock out this pin (pic 1), with a 3/32" or 1/16" punch, punching it through the hole in the bench block. This is the only pin you absolutely need to remove. This is the sear stop pin.
Note that it has a smooth end and a splined end. You want to knock it out from the smooth end. Give it a little tap or two if necessary to see which end is which. On mine, the splined end is on the left side of the TG.
The pin to its left held the safety on, which I removed.
I recommend removing the sear pivot pin as well, because it's much easier to reassemble this way; i.e. get the large spring to compress straight down.
4. Pic 2 shows the replacement spring for the mag release/sear. Stock (darker) spring on left.
Ace Hardware, bin #150, part #540449, 2.5" long, wire gauge .028", 75 cents each.
I cut it to slightly shorter than stock, which is 1.25". I used a diamond cutoff wheel on my Dremel. Insert cut-off end down towards the mag release, so the spring seat on the sear has the nicer end.
Longer will give you more tension of course, and heavier trigger pull; on the plus side, it will also give you tighter mag retention. Buy two springs and experiment.
This pic also shows the twist-tie on the trigger for reassembly. What I actually did was use this twist-tie, then another one through it, looped up to the top of the TG, to hold this one in place. Otherwise it would slip down.
5. Observe how the trigger spring fits in there. Push trigger blade forward (i.e. top of trigger backward), then push trigger spring out with the punch.
Replacement trigger spring (see pic 2 in post #8) is a BPS-5, from
these guys. This particular spring has proven very useful in a variety of guns to reduce pull weight, so suggest you get a pack of 5 ($7). Plus it's just nice to have spares. I would also recommend getting their cylindrical spring sample pack, one of each spring ($10).
6. Insert new trigger spring back into its slot with needle-nose pliers, cut end first, so that it fits into its slot, and the uncut end sits in its seat in the trigger. This way it will compress straight in. You will probably have to push the spring down into its trigger seat with your punch.
7. Vertically install the sear spring, put the sear down on top of it, and insert the sear pivot pin. Keep the sear horizontal for the installation. Making sure the sear is below the holes for the sear stop pin, install that pin. Remove the twist-tie(s).
8. Install TG back onto the receiver. Put the front screw in loosely, then the rear one, then tighten them down. Install into the stock.
Once you've done it once, it is about a 5-minute job.
Optional actions:
Remove trigger and sear completely, and polish the useful places for smoother engagement. Not sure it matters much with this design though, as there is zero creep/pre-travel to the break.