Your experience seems similar to mine: The first time I ever saw a BP/W (the original Dive Rite 55# horseshoe wing and Al backplate) and huge (or so they seemed to me) non-isolation manifolded doubles (PST LP 104'a) was during my Cavern and Basic Cave courses (NACD/NSS-CDS, in 1988). We students had to wear a Y-valved single cylinder for those courses, but our instructor wore his full cave gear and spent a bit of time chatting about his gear and why it is necessary.
Dive Rite continues to sell the 55# Classic Wing. This Wing is sized to accommodate double PST LP 104's (which are very negatively buoyant empty and have an 8" O.D.) and a couple of Al 80 stage/deco cylinders, in fresh water caves.
Your first tech cylinders will probably NOT be as massive as double 104's. I doubt you will need a 60# wing.
rx7diver