All great points. Thanks for those. When I saw the degree to which this happens at just moderate go-get'em power, l thought about the filters. I should note that these symptoms were there from the very first drive when I bought the car at 200 miles on the clock and with the 2.9" pulley. That's the only known change to the car. I'd be surprised to find dirty filters (maybe a mouse nest since the car has obviously sat a lot). But you can bet I'll be digging into the air box further and will report back. My guess right now is, it's just the wimpy Ford boot, but the stock air box is likely a bit restrictive for the high air flows we now seem to like. FYI- I'm planning a 2.7" pulley change with an updated tune on a dyno next month.
Things like this can be fun so long as everything stays healthy. I gives something to do.