(2) Assuming so, would it then simply discharge onto the the carb mounting surface of the manifold (slots in particular)? Does the center divider get reduced - removed to certain depth  - "sharpened" edge - what sort of manifold match?

I’ve experimented with the iron intakes in dropping the center divider down and those efforts end up hurting the lowend torque values regardless of the spacer design being used.  The Mummert aluminum 4V intakes have a preference for a measure of open plenum between the intake and carb and that’s what the tapered spacer provides.  On the other hand, the Blue Thunder intakes tend to prefer a carb spacer that is more segregated in design or has less openness between the sides.  Said another way, the BT intakes prefer a spacer that keeps more true to the dual plane design.  Doug’s observation mimics what I also see with the BT intakes.

With both intakes being so similar in overall design, then that begs the question “Why the different spacers?”.  Here’s my observation.  The Blue Thunder intake has a crossover slot at the secondaries while the Mummert aluminum intake does not have that slot.  Unless proven otherwise, this would be a contributing factor why the two intakes prefer different spacer designs when all else remains equal.  The verification for this would be to test the Mummert intake with and without the aforementioned slot and verify that is indeed what is driving the carburetor spacer difference.

Here are a couple of pics of some of the spacers that were recently tested on a variety of Y intakes.  The left picture is the carb side of the spacers (top) and the right picture is the intake manifold side (bottom).

Lorena, Texas (South of Waco)

you just stopped me from making another mistake

stuey