hi, don't lose sleep over this! We were all there once. Sounds to me like you are doing pretty well. I don't have the Gronk kit, but I ran a MC2150 for over 15 years, put it on in 2000. One thing you have to realize, is that on your 86, the computer controls BOTH the distributor and the carb. You no longer have the original BBD, but do you still have the original distributor? Your best bet is to replace it either with a 78-80 stock distributor, or an HEI upgrade (which is what I did) I recommend the DUI, expensive, but IMO worth it. Others have had good luck with the cheap knockoffs such as Skip White, not me.
Gronk knows what he is doing, and I'm sure your carb came calibrated real close to optimal, but probably not right on. Sound like you have an off idle stumble, running rich. Before you do anything else, the car has to be timed correctly. If the computer is still hooked up, it is trying to control the dist, and the now absent feedback carb, so I can't see how it will ever run right. Try a ECM Test bypass. I have never done this, but others here can help you with that. BTW, the computer is behind the pass. side kick panel.
As for the whistle, can't tell from here! (southwest VA), but sounds like a manifold leak. Try tightening all the bolts, there are 14 of them, paying special attention to the ones at each end of the manifold(s), which are actually studs. Could also be air cleaner seal. good luck, gz