Hi robbo i'm a bit confused here,the original manifold is a M62 1rst generation,but the one offered on ebay.com is a M90 4th generation.
I assumed the M90 has more power since it's a 4th generation design & i also recall reading from tone monday that any further S/C generation can place at risk blowing the trans which according to records by GM is capable of pushing up to 285 pounds-per square feet.
I guess the nose pulley may make the difference here isn't it ?