Although 440's were (under)rated at 375hp, somewhere there was a Wikipedia article claiming that 440's were between 400-425hp, I think regardless of whether or not it was a hp. It sounds like if the goal is 400hp, you'll make that for sure, just rebuilding it stock.
But assuming you want more than that, while staying on a budget, I can't tell you in details what a lot of people here can, but I can say that I just sold a 74 Barracuda (I'm still pulling hair) that had a mild 440, and I love that motor. All the detail is in my signature below. There can't be more than $1-2k in it in the worst case, since it's 90% stock. The best guess is that, most conservatively, it made at least 480hp, but was never dynoed. Cheers.