eh I don't have a link, but its fairly simple, open what you want to hex in brawl box preview the model you want to hex then over on the left side theres a bar click that to open the viewing options.
Toggle the polygons till you see which polygon(s) you want to hack off xD (pun...yes I know it was lame.) exit the preveiw and open the model's drop down list you'll see a category called polygons the numbers are the same as how you seen them, export the polygon(s) and then comes the tricky at first part, your going to want to open both the PAC and the Polygon in a hex editor, inside the hex editor is where your going to find out where the polygon is and here's how you do it:
look at your polygon in the hex editor and scroll down to the bottom and on the left side there's a number (that counts lines) the last number there is telling you how many lines that polygon is, note it down.
scroll back to the top and copy from the top down to something like ff ff ff ff ff...oo oo 64
or basicly the first 64 after some ff's and then go to your pac file and search the hex stream for what you copy-pasta'd
.....at this point I feel like I probably lost you so here's this you tube.