Ok, just to update my earlier comments on the thread.... I'm limited to a 1" spacer on my setup due to hood clearance. I'm running a low-profile Weiand single-plane on my 350, with an old Cam Dynamics 'super-3/4' cam with a lot of overlap.
I already had a 1/2" phenolic open spacer. I added a 1/2" 4-hole phenolic on top to basically fab a 'combo spacer' (which Wilson recommends for motors with a lot of overlap since they say the tapered variety might amplify reversion on such motors).
The results were quite good as far as throttle response and idle smoothness. I have yet to try anything really hairy as the roads here still have some salt on them, but preliminary tests have been very encouraging! My first test (in my driveway when the roads were still totally grubby) went like this: I backed out, pulled to the back of the driveway, put the th350 in D, took my foot off the brake and punched it about 3/4. I thought I had skidded in sand, but a look revealed two 4-foot patches on bare asphalt. I run 275/60R15s at 20psi in back, so the patches were pretty wide! Also, the tires are taller than normal and knock down the effective gear ratio from 3.73 to about 3.50, hardly holeshot material. I was quite pleased, especially since my little 350 isn't at all cammed for torque.
I did hit the throttle-binding problem
My gasket has bigger holes than my spacer, so I dremeled out the top of the spacer just a tad, since the bind wasn't very strong (a tap of the gas pedal cured it). It's gone now, but I'm still not sure if I was binding or if I just had the carb torqued down too hard since I was paranoid of vacuum leaks with 2 spacers and 3 gaskets. I may have warped the baseplate a bit, but if so it has sprung back with my latest (and less torquey) installation.
Conclusion: I'm interested enough to pursue this further, that's for sure!