what's the primary use for the gun? If it's an HD gun honestly I'd try to remove the ghost rings and sell them or trade your barrel for one with a bead. Then you could add the heatshield no sweat. It's not the end of the world if you can't offload them, I just feel Ghost Rings are better for slugs and ranged shooting...something that'll probably not come into play and could get you into a trouble in an HD scenario. They're fine up close but I definitely prefer the bead for buckshot applications. I'd honestly call around and get gunsmith quotes on how much it'd be to have the Heat Shield put on. It may be cheaper than you think, maybe not. Give it a try.
If you are ready to take the shellholder plunge, I can personally vouch for the Tacstar. It's a great product in my experiences on the Remingtons, Winchesters and Mossbergs I've had them installed on. The use of blue loctite on the knut and screws helps as well. If you do install one, do yourself a favor and definitely save the original ejector screw and trigger housing pin. If you want a neoprene buttcuff shellholder for the stock, make sure you put it opposite the inside of your shoulder.. Right handed, right side of buttstock, left handed-left side. I used to slip the buttcuff over the stocks of the 590s and solder through it just enough to expose the sling stud in the stock. Be careful and take your time and it can look pretty clean.