1995 Chevy Astro alignment

I just put a down payment on this van, and the sales dept said they'd fix an obvious brake problem, and have it re-aligned. The alignment shop couldn't bring it back to absolutely correct, and noted that the frame had been welded. It pulls more than slightly--although the dealer says this is entirely normal--but it is to the left, not to the right as it should, and it travels over 3 lanes to the left within somewhere around 200 feet or so. If it can be aligned back to where it was, and not chew up tires or be unsafe in any way (that is, the frame falling apart) then I'll keep it, but otherwise will give it back and call the down payment the price for the lesson. What do you think? Can it be safe? Is frame damage irrepairable? How can I tell? Thanks very much.