Tank modifications

Well, I sent my tank out to get hydro tested and the tank itself is fine. The problem is that the stem of the reg broke off when they were taking the reg out. I figured this would be an easy fix since the stem wasn't stuck inside the tank and I could just throw a new reg on but of course, with my luck, I can't do that due to a strange problem. The metal ring that goes around the top of the tank itself does not fit flush against ANY regulator (tried a couple brand new ones at the store) even though these regs fit fine on other tanks. The old one broke so I obviously can't use that, my solution is to grind the top of the tank so that the surface meets the reg evenly, that way the o-ring on the inside won't pop out when you try to fill it. The real question, and reason for this thread's existence, is to ask if this is a dangerous idea or if it's as simple as I think it is.

I'll try to upload some pictures so I can show you the part in case my description wasn't good enough. In the mean time, here's a picture I found with a search that shows the piece (link). The piece I'm talking about is the silver area to the right of the black regulator. That's just a chunk of metal attached to the actual tank which is why I don't think it would hurt to grind it a little for a better fit but I thought I'd check with the more knowledgeable members of the forum first. I plan on grinding it to be at the appropriate angle to fit flush with the reg and then smoothing the surface out if necessary. If you know of any reason why this would end in disaster (or even if it would go fine) please let me know so I can get it done or replace it.

It was a crossfire tank. The guy at the store told me that crossfire puts a buttload of red loctite on the threads of their regs so the stems sometimes break off when they try to remove the reg. I'm not sure where he sent it to get tested. I would think that a little heat could have prevented the reg from breaking but I don't have much experience with this stuff so I could be wrong.