[HackD]

If it is an ICS, it does not have pins. It has a grub screw affixing the front sight to the barrel - recessed in the bayonet lug.

If it is an ICS, the receiver threading WILL present challenges. It uses Imperial measure threading (90% of the time, if not better) that will require a RS sized delta ring (G&P part, is my recommend) and a compatible RIS designed to use the delta ring as the rear attachment point.

I have a Madbull Noveske 7.25" RIS on my 10.3" .. i believe it was imperial threaded ICS, but by luck, i had the metric threaded Madbull Noveske nut force-threaded successfully onto the receiver threading - it could well have broken the receiver or stripped the threading if blind, dumb luck hadn't intervened in my ignorance.

My 14.5" ICS has a Mk18 7" Daniel Defense RIS mounted, of the type that uses the delta ring to secure the RIS. I used a G&P delta ring to replace the undersized/odd design ICS delta ring. The G&P is an imperial threaded delta ring. This M4 was put specifically together to carry a barrel mount M203, so the selected RIS was pretty much a mandatory requirement to make work.

It is doable for the ICS series, but you need the right combination of parts, and you will likely need to do some sanding and filing on the barrel flange (stock, or otherwise) to get the whole assembly to work nicely together. This isn't a newbie friendly procedure unless you are confident in yourself, your skills, and in use of hand-tools to modify things. You might be better off selling the ICS, and getting a TM compatible M4 version, or a G&P (or similar) already setup to your aesthetic desires, otherwise.