I have a 70SS with a 396 / 350hp. I want to change the manifold and replace the Rochester with a Holley. My concern is with the cowl hood. Is the height of the carb going to fit?

I don't think there will be any problems, some of the 70 454's (LS6) had Holleys on them and they fit.

Depends. Your intake may be tall enough that you need to use a smaller spacer (1981 injected Eldorados use a spacer about 3/4in tall) or you may need to eliminate the spacer all together. I just finished a SB400 installation using a very early Z-28 intake with a Q-jet, and I had to eliminate the spacer between the carb and air cleaner. Just roll the dice and see how it fits.

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Just don't buy a high rise manifold and you'll be safe.

-Joe Y.