What kind of brake pads for Dia Compe centre pull brakes
You can use V-brake pads, but they tend to be longer and can create clearance issues. On the bike I currently have set up with those pads on Dia-Compe centerpulls, the shoes hit the fork when the brake is open, making wheel removal difficult.

edit:

As ojs notes below, road caliper pads are probably your best bet. They also tend to be on shorter posts, so they don't limit tire clearance as much as V-brake pads.