It will NOT fir the stock headers. The T4 design is considered old school on the V-6 engines. At least on the street cars. They spool slower, being a P-trim and a .81 A/R.
lt should fit any 76 trim ex wheel and its very common these days for racers to convert to a T4 tangential housing if they are looking for more hp due to the 3 bolt housing being a major restriction. It could be adapted to stock headers but not worth it imo since you really need to be limited by a 3 bolt for it to be worthwhile and a dp with external gate must be fabricated. Most run aftermarket headers with a T4 flange when they have gone that far.