All the chassis mounted tube sockets on the Mark III and Stereo 70 are octal sockets, not nine pin. I'm not sure about the ST70, but the Mark III has holes which are slightly smaller than your average eBay Chinese tube socket. You need to be careful when you order sockets, or they might not fit in the hole.
These sockets from Triode Electronics fit perfectly and seem to be of very good quality. The only downside is they cost a little more.
http://store.triodestore.com/77-mip-8.html
If you are talking about the nine pin sockets that actually mount
on the circuit board (the ones for the small signal tubes), I'm not sure it matters exactly what size they are. They mount on the top side of the circuit board, and they don't need to fit through any holes in the chassis.