Everyone knows that the Hulk cope with a devastating amount of punishment, and has been shown to be very durable, energy resistant, heat resistant, cold resistant, and psi resistant. So is Mangog, but there are a couple of things that Mangog can not do as far as I know.
1. He lack a healing factor that can bring him back from being just a stomach, and bones to healed in less than 5 minutes.
2. he lacks dynamic strength augmentation like the Hulk has.
Anyone that has read the Hulk over the last 4 years has been witness to the fact that he no longer takes minutes hours or days to go from base to planet destroying might. His power set says that he has no limits to the amount of strength that he can attain. Mangog does, as does Thor. What we witnessed (well at least those of us who read Heart of the Monster) the Hulk do in the Dark Dimension was not the Hulk's full strength capability, and according to the characters bio, he could have trumped that level by an exponential amount. This is not me being a fan boy, but taking what has been canonically written about the Hulk.
The Hulk has been shown to become more durable as he grows in power. For instance; when the Bi-Beast, Wendigo, and Arm'Cheddon assaulted him, he didn't even wince in pain, actually to the contrary, their combined assaults did not even register. These are guys that would not just make classic Thor wince in pain, but launch him though whatever architecture, or real estate present on site.
This is not meant to be a low blow, just an example. There was a time, that the Avengers Mansion came under siege by the Masters of Evil. Hercules was put into a comatose condition, by taking a huge beating. Thor enter the scene and mops them up, but before this happens, he is hit by Mr' Hyde, who runs into him, and visibly hurts Thor. Hyde passed out from running into him, but it still hurt Thor.
Thor would simply not be able to shrug off the combined assault that did not even register to the Hulk. These are confirmed class 100's, and they weren't even able to budge the Hulk. He was more concerned with Betty.
Rage says that the Hulk would not be capable of tanking the G-Blast, but I say that it depends on how strong the Hulk is at that point. You simply can't ignore what happened on panel in terms of the Hulk's strength amping his durability.