I recommend Ron Francis.
Ron Francis Wiring
Had a friend who builds Hot Rods recommend them to me. He mentioned he had very good service, quality, and fit from Ron Francis over Painless.
After buying and installing one in my 65 Mustang, I couldn't agree more.
The Express system allows you to run individual circuits, rather than all the wire hanging out the back of the fuse panel. Here is a link to the Mustang specific harness.
http://www.parts123.com/parts123/yb....Z5Z5Z50000278a