A 512 kit doesn't need a big bore, so the sleeves won't be an issue. KB will ask you what bore size you want and use a sleeve that will still have room to grow. Mine is 4.500" bore and has the ability to go to 4.530". Your 512" will probably only be 4.375" bore.
The only real downside to an aluminum block is the initial cost.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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