It will be fine. We are cutting down weight with the engine, and the axles will be beefed enough. Like what was mentioned, there are a ton of 1000 HP Mustangs running big slicks and beefed 8.8s and they have no issues. And yes, they do run deep gears, most of them seem to be in the 4.10 to 5.13 range from what I have seen at the track. Plus... he's not running big heavy Swampers with big lugs. They are just MTRs.
Lets get one thing straight right now. Do not come in here and tell me what will or will not work when you have no idea what you are talking about. I don't have time to argue about it. Just like the mustang comment. No idea what you are talking about, especially when you even say "I don't think." The 8.8 is a dang strong axle if its built correctly. Both axles will be as good as a stock Dana 60s with 35 spline shafts.
Yes, everything is breakable, but we aren't using junkyard stuff here. This is all tip top of the line parts.
Can this engine break every last piece of the drive train? Yep! But with some sense it will hold up just fine. Its like driving your car. You don't get in it and floor it everytime you take off do you? I believe the saying goes "just because you can, doesn't mean you should."
Oh and by the way... the XJ that ran in the Ultimate adventure last year was running a 400 HP LS1 with a DANA 30 front and a DANA 44 rear on 37s. Now, they of course were beefed all they way too with cryoed R&P and RCVs etc, but the interesting thing is that through the entire trip, he was the only person who did not break anything. This rig will have another 50 hp or so, but it will have stronger axles to support that...