Thor-Agena D used a "standardized" Agena D upper stage that was designed to fly atop Thor, Atlas, and Titan with minimal changes.
The SLV-3 was basically an Atlas D core with thicker tank walls to support the weight of upper stages, as well as uprated engines.
Ed might like to know that I found a couple of mistakes/omissions on his Space Launch Report failure list.1. Pioneer launch 8/17/58--"Thor turbopump T+28 seconds, RSO"[etc.]
Definitely need to update those lists. I started that project in 1998. Much of that information has been updated by declassification, etc., since.
3. Corona 99 R&D 9/2/65--"Agena failed, RSO"This was the famous failure where high wind pushed the booster off its flight path and debris fell on a trailer. The payload, a mishmash of scientific experiments dubbed MPRV, had nothing to do with the Corona program.