46 heads were on a 350 and a different 46 was used in 1969 on 2bl 400s and 428s. I would think for street use either 46 would be a good choice for decent pump gas compression ratio. Probably about 9.25.
IMO, If the 389s original heads were from 66 or earlier, the 46s would be an upgrade to better breathing and more reasonable compression.
I dont see original 64-66 GTO heads useful for anything but an accurate restoration.
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