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We've been using A-body headers for years. A mini starter helps with some clearance. The biggest issue with the 'cheapie' headers of any brand is the flange, so we cut them in two places and use Remflex gaskets and have had no issues.
Rather than mess around with moving the gas tank for duals, we use the T/A style mufflers and exit just before the rear wheels. The only down side is there is almost no room for resonators, which they kind of need unless you like the rumble.

Have him check or forfmjbodiesonly, if he hasn't already.