fyi
'3 bolt' turbos are called that because of the number inlet bolts where the turbo bolts to the header , not where they bolt to the downpipe
a "4 bolt turbo" has a square flange to the passenger header ( typically used for higher hp turbos over 76mm and on imports and deisels ) and a 3 bolt has a triangular flange which is the standard config for the turbo regal
a sfor downpipes there the 4 with wastgate provision like we have standard on the turbo regals , a 5 with wastgate provision which is imports , then there the external gate only styles.. vbands and the old old school perfect sqaure 4 bolt pattern with a round flange called 'on center'