Don't some of the older rams horn exhaust manifolds (like for 327's from the early-mid 60's) have an alternator bracket cast in? Maybe that would work. Some of those are 2 1/2" outlets, too, but they're harder to find, I think.
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1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.