As you know, the Atlas system is based on a single heavily webbed and rigid girder that everything is bolted on to. I would think anything which compromised that would render it useless, and personally I wouldn't even try a repair, unless you have the 48" bed, then you might be able to cut it down to a much shorter length and get rid of the bad bit. You would only need to shorten the leadscrew and drill a few holes and you would be back in business.
But all is not lost, because of the way it is made, just replacing the girder would bring everything back to spot on, especially if you could get the top face of the second hand part ground up.
Over the last year or so, I have noticed that some 10F's can be picked up for well below £100, and that would make a very good donor for the girder, plus a spares bank as well. The 10F was made in three different lengths, 36", 42" & 48", mine was 42". If you do manage to find one to replace yours, you would need to make sure the leadscrew matched for length, as mentioned above. I managed to buy a brand new 48" screw for mine, and cut it down to length.
As a starting point, I would put an ad on here to see if anyone has one in the back of their shed. Don't forget to say please and thankyou.
Sorry I can't be of any more help. When I sold my machine, all my contact addresses for spares went with it.