Good luck, you crack open a perfectly fine ARP9 to install those bits, unless done by a really good tech you'll have months of issues and ultimately end up replacing it. Even then, a good tech will advise against most of them.
Those parts are shiny to attract the unsuspecting youth magpies.
Heres actually a better idea - get him a polarstar jack and HPA setup.
Power will be adjustable, ROF will be crazy if it's tuned by even a simpleton, has the cool HPA factor and will be a lot more reliable than a teenagers pick list of shiny bits.