The client has two sites. One of them was "killed" about a year ago, there is no content any more and the domain root is now redirecting to client's other site using 302 Temp. Redirect.
The site that was killed has approx. 650 links pointing to that domain root. Since 302 does not pass link power, we want to change this redirect to 301 Permanent Redirect.
The second client's site is on the same theme, so there would be absolutely no problem here. However, how would Google look at suddenly getting 650 links to the other client's site?
Currently both sites are on the same IP, whereas the killed off site actually does not exist, it only serves 302.
The whois info is not the same either - the killed off site has whois of web development agency of the client, the other (live) client's site is registered in client's name with their web development agency being Tech. and Admin contact.