Let me start off by saying that my expertise is in domains proper – not websites and certainly not SEO. So I can't say with absolute certainty that a whois change won't affect Google rankings. Nobody CAN give you that kind of reassurance, since Google's algorithm is so inscrutable.

What I can say is this: Whois changes are normal. Established companies often reassign the contact info when an employee changes roles. Likewise after rebrands or mergers or buyouts. More often, they simply reformat the whois, going from "Smith, James" to "James Smith" or "Jim Smith", updating phone numbers, standardizing old idiosyncratic email addresses, and so forth.

Google would be insane to penalize whois updates per se. Insofar as Google's algorithm picks up on whois changes, this may alert the system to a possible ownership change. So maybe, just maybe, the algorithm re-evaluates the site's trustworthiness at that juncture.

But a change of ownership is no reason to penalize a website either. It's much more important to look at the website itself to see if anything a visitor sees is concurrently changing. THOSE changes might upset earlier rankings. A rebrand, for example, can damage SERP rankings if URLs aren't handled carefully, if old links are broken and Google mistakes the site for something entirely new.

In all the thousands of articles I pour over in the domain industry, I've never come across a story of a website losing its rankings after a mere whois change. Never. After a domain name change, yes. After a website overhaul, yes. But not after an update to the whois database.

Google has been around the block a few times. Their algorithm has dealt with websites being bought and sold before. When domains change hands, that invariably entails a whois change. So it would be idiotic for Google to downgrade rankings purely on that basis. It's unlikely, therefore, that they do.

Searching for instances of such catastrophes just now, I couldn't find any. The consensus among professional SEOs, based on a few articles I've sampled, seems to be that whois changes ought not to coincide with other large-scale website and branding modifications.

Of course, you should do your own reading. And consult with an SEO professional. But I suspect you're more nervous in this case than you need be.

One option might be to ask for whois privacy to be applied during and after the escrow holding period. That would mask the ownership change once the website is paid off and the domain comes out of escrow.

But note this: Some whois privacy services invent a long random string of characters for use in the email address proxy. Those random strings are automatically updated every so often. If Google really were fanatical about punishing whois changes, then such whois privacy services would be driven out of existence. Yet they're still here. Conclusion?