Bob,
My sense that the eBay '66 frame is likely a P-13 is a guess based solely on the chrome lugs, since we don't know what parts came with the bikes. As with just about any Paramount, there's also the possiblity of a custom job. Pre-1970 P-13's are often misidentified as "touring" frames (i.e. P-10's) even though the P-10, P-15 model Paramount didn't exist until the 70's, as you noted. Basically, what had been the P-12, P-13 frame became the later P-10, P-15 - i.e. eyelets, braze-on TT cable guides, and also the fork rake, which has a more dramatic bend close to the fork ends. Pre-1970 P-12 and P-13 frames commonly have all of those features. As you also mentioned, by 1972 or '73 at the latest, we have what we think of as the "modern" P-13 - cable clips instead of braze-ons, no eyelets, fork with more of a subtle dogleg than the late-breaking "rough road" bend, and also 3/8-inch shorter chain stays, and probably a lower rear brake bridge to accomodate the optional Campy brakes. There are actually some interesting "transitional" P-13's circa 1971 or so that have some of the features of the "new and improved" P-13, but not all - i.e. they have the?older fork rake. I think the eyelets were gone on the P-13 by '71. Whether there were differing bridge heights on the pre-1970 bikes is something of an open question, as is the question of chainstay length. I think the evidence at this point favors the pre-1970 frames generally having the longer stays later seen on the P-10, P-15. That eBay frame is pretty sweet - no question about that.
Ed Granger
Lancaster, PA, USA