Yes, the Riffle Shuffle stuff is scattered.
Back in the good, old days, the strongest incentive to learn a false riffle shuffle was to perform versions of Triumph" and Dai Vernon's version in Stars of Magic (1946) was easy to learn and master. I was familiar with Charlie Millers Strip-Out False Shuffle in Expert Card Technique (1940), which was published six years prior to Stars of Magic. You can check this out, but nothing is really mentioned about culling or block-transfer work. Dai Vernons More Inner Secrets of Card Magic didnt come out until 1960, a year after Marlo released Riffle Shuffle Systems. The other explanations of false riffle shuffles I had skimmed were Hilliards Greater Magic, Buckleys Card Control, Simons Effective Card Magic, and The Card Magic of Le Paul. I fiddled with Le Pauls description, but I was satisfied with Vernons easy version. In discussing shuffles with other cardmen, I was told that the key principle and dynamic in riffle shuffle work is the culling and block transferring. As others have suggested, locate, borrow, study, or buy Marlo's trilogy. Only the first one, RIFFLE SHUFFLE SYSTEMS, is easily available. (Check my Website: www.JonRacherbaumer.com).
THe other two are sometimes available through used book dealers. I plan to release them this year.
As also mentioned, Karl Fulves manuscripts on Riffle Shuffle technique are worth getting: Riffle Shuffle Technique - Part One Two (Epilogue - 1975), Riffle Shuffle Technique: Preliminary Notes On Part One (undated), Riffle Shuffle Technique: Preliminary Notes on Part Two (1973), Riffle Shuffle Technique - Part III(1984), Faro & Riffle Technique (1974), Riffle Shuffle Set-Ups (1973), Setting Up Exercises (1995), and Riffle Shuffle Controls Part Two: Blocking Off (1996).
I particularly liked the last one.
I hope this helps...