I'm wondering if I am the only person here that has ever actually seen a photo of Y-10?
Leaving aside things like lack of several pixels of contour below the 002 number on tail or heavy corners on the pylon of outermost engine...
Probably the most obvious differences between 707 and Y-10 was Y-10's prominent "forehead" above cockpit. While on the 707 top of the fuselage was getting lower immediately forward of the passenger cabin, on Y-10 the "roof" was straight almost to the point above the pilots seats. Another prominent difference was that Y-10's vertical stabilizer was taller and somewhat less tapered that on 707. And the cockpit windows - to me the pillar separating that aft-most big square window and that triangular one seems essentialy vertical (from "our" perspective to me).
Of course, unfortunately there's a scarcity of sources for Y-10 - there seems to be just one line drawing (originating probably from Jane's and of very suspect accuracy indeed, but still better than pure guessing - IMHO cockpit there is bit too high and too far aft) and number of photographs is also quite limited. BUT THEY DO EXIST, AND CAN BE FIND BY ANY PERSON CAPABLE OF USING GOOGLE.
So... NO... simple repainting of 707 is not the proper way to depict Y-10.