’91 ish case 1840 looking to add aux. hyd. question on valve (power beyond?)

Hi, new to the thread. I don't know if anyone on here has experience working on a 1840 or 1845 skid loader, but I have a question. Our machine (a 1991 1840 if I remember) does not have auxiliary hydraulics and we would like to add some. To add them the factory way would require about $2000 in parts. I have found a kit that uses the power beyond on a loader valve. My question is what is this cap on the valve? Is it a relief valve or an add on plug? Any help is appreciated. Here's the kit from Northern; https://www.northerntool.com/shop/t...200724096?utm_source=CSE&utm_medium=Shopzilla