I ran back towards Arefu and found a bridge overhang where I didn't think the Huge Mutey could follow - however if I went under on one side, he would run around to try and get me on the other. After killing the 4-5 regular Muties that followed the chase and with half my health left - going back and forth the big boy I dont know how many times - I hit the huge Mutey with at least 300 rounds (FWE weight restrictions keeps me from carrying more ammo) from all my guns - I normally carry only 5 guns and 3 were out of ammo and the other 2 had less than 50 total left.
All those rounds didnt kill him yet though as a group of 4 Wannamakos jumped him along with 7-8 radscorpians & 3 mole rats & 2 meriluks went into a big battle together. The huge Mutey won as all the beasties were killed by him usually taking just 1 swipe at each creature. However, the Gargancuan was down to just 1 bar of health and all I had left was my 10 mm & shotgun. I came out of my hiding place and I emptied the remaining 10 mm rounds into him and on the last shot with the last 10mm bullet to the head I finally killed the Huge Brute.
On the way back to Arefu I ran into a pack of wild dogs and with my remaining shells in my trusty shotgun I killed the entire dog pack with all but a few shotgun shells to spare! I have never used so many bullets in 1 battle in my entire fallout experience! Hopped on the motorbike (FWE fast travel method), went back to Megaton and called it a night! Just thought I would share why I like modded Fallout so much!