For extra clearance for multiple carbs, or fuel injection systems these brackets are your best bet. Bolt to the heads and water pump.
For the 128R the alternator will fit all 1969 and newer heads and the 228L A/C compressor bracket fits all GM aluminum heads and may be used on 1969 thru 1986 cast iron heads by drilling and tapping one hole for the upper mounting point. Will clear up to 3 inch tall center bolt valve covers when using 1987 or later aluminum heads or clear up to 3-3/4 inches when using 1986 and earlier heads.
When using 1986 or earlier heads use the 112R and the 212L. The A/C compressor bracket is used on heads with one bolt hole and will require drilling and tapping one hole for the upper mounting point. These brackets will clear valve covers up to 4-1/2 inches tall.