the stock 2.2 manifold is so restrictive that even polishing it wouldn't help out a whole lot. Unless that is the ones with air injection are an improved design. your best bet would be to hold out for a header that works with your configuration, or at worst get your extrude honed. there are angles and areas that you will not be able to reach with a grinder or flap wheel on a rotary extension, but extrude honing will get it all for you.

at this point though, the cost is going to negate the appeal of running an lsj manifold anyway, so save for a better designed unit.

 

Polishing it wouldnt do much good for it because the collector at the end is so small. It be extremely hard to get anything inside it to polish the inside. The ss manifold had a larger collector on it which made it easy to reach inside the whole thing.