Hastings has a gold trigger replacement trigger group complete with steel guard- that's the one you want.

Additionally, you can try various factory trigger groups as the trigger pull characteristics varies widely from one to the next- keep trying until you find a "sweet one".

I am doubting you can improve much on one ragged hole at 100 yds with 12 gauge slugs... Pretty good IMHO.

I wouldn't want you to think I'm crazy

In my area many counties are shotgun only for deer. I use my Rem. 870 which shoots Lightfield sabot slugs so well (ragged hole at 100 yrd.s) with a Leupold scope & Hamilton barrel that it has occurred to me that the gun's heavy trigger pull is probably a limiting factor. Does anyone know of a replacement trigger or trigger lightening procedure for the 870?

Get it to a Gunsmith.
It's not the cost of the parts, You don't want any 12ga slugs going astray.

I believe Canjar made a drop in unit at one time, but I haven't seen one advertised in quit a long time.

The way to lighten and uncreep the trigger is to reduce the sear engagement. Whether you want to tackle it yourself or not depends on how handy you are. If you can take apart the trigger assembly, put it back together and it still works, I'd say go for it. The sear and hammer on an 870 are not expensive to replace if you totally screw the pooch.

The hammer pin is staked and doesn't take well to being reinstalled. You are better off putting in a new one.