I have been running a Cool Carb heat shield and two spacers for 5 years now on my street 340. You can definitely feel a difference in the temp of the bowls before and after. But you have to be careful because they have a max temp of around 275-300 degrees. They will melt if you get them too hot which another member showed me back when I was looking into buying. But mine still look to be in great shape when I last took the carb off over this Winter.
1970 YO7 A66 [Canadian Export] F8 Challenger
340 (SL.P. 226/238@.050,270/288 dur,.538"/.528" w/Yella Terra 1.65 rockers, 9.7:1, 63cc Sidewinders (Bowl Ported),RPM intake, QF SS-750 Annular DP, MSD Street Fire Ign., & TTI's. 727/Dynamic 9.5" 3800, TF-2, & 3:91's