There was a similar Harper setup on ebay last summer. Here is a link to the thread discussing that
Harper discussion and some comments about its use. I still have mine, and I'm planning on using it in my next retirement project.
Some experts will tell you that the Harper arrangement does not make the best use of the available carburetors since, as stock49 observed, each carb only supplies one pair of ports. As the forward (1 and 2) and aft (5 and 6) cylinders do not fire at 360 degree intervals, the airflow pulses through the carbs supplying those cylinders are unbalanced.
Other experts (e.g., Smith and Morrison's Scientific Design of Exhaust and Intake Systems) claim that the use of three nearly-isolated carbs, like the Harper, performs quite well on an inline sis (page 187 in Chapter 9 of my paperback copy. I've never seen any dyno or road tests that sort through these questions.
