I had a spare Edelbrock 1406 lying around, so I tried these restrictors on a 289 once and hooked up my wideband. The Mixture was WAY rich, even after I leaned it down quite a bit. They might eventually work with a lot of messing around, but I believe (it's been several years) I started with a base tune for an Edelbrock 1403, which is a 500 cfm carb, and it wasn't even close. I believe I just swapped back to the normal venturi cluster.
Of course, there's always the chance I screwed something up. In fact, if I recall, one of the restrictors went on a touch cockeyed for whatever reason, probably not enough to make a difference. I don't know if it was an operator (me) or machining error, but I remember that the epoxy set up before I could do anything about it. And I think that's the danger...it's pretty easy to ruin a primary venturi cluster if you don't like the result, so plan accordingly. As always, your results may vary, as I'm a professional English teacher and amateur mechanic (who does, to be fair, do almost all his own repairs).
I'm running an actual 1403 on the car now, and I don't think there's much of a difference in throttle response between a 1403 and a 1406, for what it's worth.
