Anybody here replace bearings on an old trackhoe?

I got an old Hitachi ZX 40 UR (Grey Market machine, about 5 ton) and apparently got a leak at the hydraulic final drive sprocket, and disintegrated the main bearing. Could only go an inch or two in each direction so was stuck in the field on this one. I opened the 3 "drain" plugs on the outside face of the hub cylinder and nothing but dirt came out so the seal at the frame must have went bad and lost all the gear oil. My bad for sure but took the track and sprocket off and tried to pull off the cylinder drum but it was all jammed up with broken ball bearing material but eventially worked them all out but the drum still won't come off. So looked inside the middle drain plug and there was a 4MM Allen bolt that apparently was holding the drum from coming out. Then things got interesting. The Allen hole had rounded off corners and I could not get it out and only had the aprox 1" diamer hole to work with.. OK, I figured I would just need to go the "Easy Out" way, went to Lowe's and got their kit plus an extra 1/8 drill bit that the salesman said was the hardest bit they had, harder than cobalt, titaniuim etc. That is where I hit the brick wall. The bits would not even begin to nick this bolt which must be a grade "super" eight bolt!! I then tried to take off the aprox 8" diameter face cover using a dent puller and heating up the rim and doing a lot of light tapping around the circle but this thing won't budge.. Any suggestions on these issues? I am dead in the water till I get this apart and get the big bearing so I am on the road again. I did throw some used motor oil inside the drum and now the drum turns just fine in both directions with no noise but obviously I need to get the new bearing in. Thanks