Not very helpful here through...It's been years since I messed with SUs, but my understanding is the dash pot oil viscosity has an impact as it helps to control the speed in which the piston raises up from the increased vacuum. I believe a thicker oil will reduce the lean spike as it slows down the rise speed, keeping it from suddenly leaning out. Experts will have to pipe in here. This may be the same idea behind the springs.
Good idea on the wideband... I find them invaluable and have had one for years. My engine is high compression with a high lift cam and for whatever reason is very sensitive to minor changes in throttle position. I'm still working on getting my enrichment settings to respond appropriately to those little changes so I don't see/feel lean spikes, and that is with FULL control over things and data logging to pinpoint it... you may struggle some with that cam and SUs...
BTW, as I'm sure you know power is found in the ignition timing... you're the kind of owner that might be interested in the Megajolt controller I have sitting in my tool box unless you ever decide to go with a 123 dizzy... it's just the controller, not everything you would need to convert to a crank-fired system, but with your obvious skills you would have no problem modifying the necessary parts (uses Ford EDIS components and a modified crank pully). It's not doing me any good in my tool box, so let me know if you're ever interested. I'll be honest though, a 123 dizzy would be much easier if a little less accurate.
