He bought a receiver and possibly a bolt that can be used for a custom hunting rifle, with a lot of work and a lot of money needed to achieve the goal. The rest, sadly, is now worthless.
Were it in original condition, it would be a find, but the sloppy "sporterization" combined with the rust throughout makes it a rifle of exactly zero value, unless he puts far, far more money into it. And even then, he'll never be able to sell it for anything but at a loss.
Think of it as someone with a beginner's course in welding under their belt "customizing" a Model T or Model A, then expecting it to be worth something. It will NEVER be worth what an original would be, even if the work done somehow actually does improve it, and the "work" done on that rifle (and subsequent neglect, evidenced by the rust) was more damaging than simply doing nothing at all.
Hate to say it, but your brother got took. How badly remains to be seen, depending on what he paid for it. Hopefully, he paid no more than 50 bucks for it, 'cause that's all it's worth, and I may be too optimistic even then.