There are several sources, including where you were at
http://www.median-line-study.com/free-download/ where the result is a 4.0mb PDF. It's also freely available in other first-page Google results in various forms. I'll post the file right here if that's allowed.
(And no doubt about it, that web site looks absolutely HORRIBLE. Wouldn't be the first one though, to still contain useful information. What's that saying about books... and covers...) Anyway he studied a controlled implementation of median lines in the grains markets between 1990 and 2005 with results which confirm previous stats by Timothy Morge, himself having confirmed those of Alan Andrews in his own publication which I don't have on hand.
The age of this method isn't the issue here, so I won't debate your prejudice against the 1960's.

I'm just showing you a specific example of a statistically significant use of price alone, which conflicts directly with claims that price is purely random. To dismiss those would dismiss as coincidental the proven concepts of trend lines and mean reversion which is why I have yet to reconcile what I read from other credible sources and from random proponents including yourself.
(You might also encounter a book on median lines by Patrick Mikula - that one is just detailing his comprehension of the Andrews course, no useful empirical study there.)
Back to your other point: how would you characterize a "successful prop firm"? The term seems to have a very broad definition (from overseas high-leverage small-game predators to full hedge funds) and I was never able to find anything compelling for me, except maybe Bright but their web site (talk about books with bad covers!) talks about future events in "March 2013" and "October 2014", so I wonder if they're still even active. One or two closer to where I live, with barely a web site at all, not inspiring for what's now a high-tech game.
Edit: typos