The compressor rear bracket (left brkt in your image) mates with the power steering pump bracket (not shown). The small bracket at the left front of the intake manifold is the factory lifting eye (pictured below in its entirety). Two 1.5" long bolts fasten it to the intake and one through-bolt & nut attach it to the upper compressor bracket to help anchor the compressor.
The R4 generates enough vibration, amplified by the standing wave that develops in the V-belt, that procuring or fabricating the missing manifold bracket, in my opinion, is important. Otherwise, the upper compressor bracket is anchored to the engine by only one 3/8" diameter bolt and the 1/2" X 11" long bracing rod.
The missing intake bracket is made from 3/16" thick mild steel. All bolts should be Grade 8 - flange head preferred. Don't compromise with bolt length; arrange for the greatest penetration into the cylinder head casting as possible. Condition the bolt holes with a 3/8" X 16 bottoming tap to ensure maximum use of the depth of the holes. Apply torquing compound or other lubricant to all of the bolt threads, except the second-back intake bolt, which should be coated with Teflon paste thread sealant or #2 Permatex.
I'll be checking in periodically over the weekend, if there are additional questions.
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