Personally I'd get another frame. Not that hard of a swap and could be done in a weekend if the other frame had the running gear on it. What is bad is what you cannot see. It looks like the metal is thin along with being cracked. I wouldn't want to put time into it just to have it go bad somewhere else a few miles down the road. The car looks to be in decent shape so it would be worth sticking a frame under. You will also have less time invoolved by swapping one out. The safety factor is the biggest plus.