That's a very powerful system. Greg, I'll defer to your judgement about the age of the unit, but I would have never suspected it was from the 1960's...they were still making those units in that color into the 1980's, and I always thought that the 1960's units all had the old single-fan design. The T21 and hose are other clues, though those obviously could have been purchased at any point. The only thing that dates it '70's or prior is the label, which by the 1980's I believe had a Canada address for Lindsay Mfg.
Search YouTube for "Astro-Vac" to see a video I made on one of these systems...I installed this 1980's Astro-Vac Mark III in a friend's shop. It's the identical system with a different name on it. Very powerful, but LOUD...he didn't want mufflers on the exhaust (doesn't like his neighbors I guess) and you can see the result.
Just make sure and keep the screen clean. A secondary filter pad on the screen, if not already installed, is definitely recommended - it'll keep the motors running quieter longer.