I have a Remington 870 that I would like to get converted to a tactical version but I cannot remember what firm does that kind of work. Can anyone help me out here?
There's several places that can do the work, or you can do it yourself.
Check out Vang Comp, or Scattergun Tech for the high end tactical shotgun work.
I agree, the best way to go about it is to do it yourself. Most of the stuff you can do to an 870 is very simple. Some of the most common mods are.
Side saddle and or buttstock shell holders. www.brownells.com or local shop
Choate or other stock. brownells again
white light. surefire.
Buy a 18.5 barrel if you don't already have one. Pick rifle or bead sight. For ghost ring see below.
The above are all easy to do yourself.
Mag extension +1/or 2. Check and see if you have two dimples on the end of your mag. If so, you will need to remove them. It's easy if you have a drill and/or dremel. Be sure to get a good spring and remove any hunters plug, dimples, burs.
Sights. If you want to upgrade to ghost ring you will probably need a gunsmith to do this. If you intend to do this I would get the bead and have the front and rear installed to match.
Pattern improvement. Test fire your gun with assorted loads first. If none satisfy you, you have a few options. Vang Comp has a huge reputation for pattern improvement, so does there price. 870 barrels are cheap, try a different one. Or you might be able to find a smith who will backbore, cone, or thread a choke system in. I think Scattergun.com has some of these options as well. Both seem to be outstanding companies. They will build, install, or modify to suit for a price.
The more you do yourself the more you will save. Personally I would only do the things you can do yourself. A shotgun is pretty simple and effective as is.