Most people install the NA1 headers onto their NA2's, then use a custom adapter in place of the catalytic converters; I believe the prospeed high flow cats offer a unit that serves this purpose.
As for NA1 headers... cost becomes a factor, one consistantly recommended unit is the mugen header, also there are the gt-one headers, FJK, taitec, comptech, supersprint, dc sports, dc sport knock offs, etc.
Performance gain on a 3.2L will be marginal, so most people tend to leave them alone. If you have a flow concern, perhaps CTSC, etc., then the upgrade would make more sense, if you have the v5.1, Gt-one claims their headers were flow tested with their v5.1 exhaust to ensure maximum performance, so this would be the unit to buy.
