removed the 305 installed carbed 350 i was thinking about going with Dynomax 89009 header back kit. but am unsure what headers to use the stock manifolds bolt holes are about 1/3 inch longer on the passenger side rear so i know if i ordered a set of shorty headers for an 85 id have same problem so what im asking is what headers do i need to get....???

 

If you get all your exhaust for '86-'90 TPI single cat application - headers, cat, cat-back - you'll be getting the "good stuff". No issues with routing, as it wasn't the chassis that changed over the years. You might need to modify a hanger or two.

IMO, the 89009 is not the "right stuff". Note the instructions say, "THIS KIT WAS DESIGNED FOR DYNOMAX HEADER #85012. IF THE KIT IS BEING INSTALLED WITH HEADERS OTHER THAN LISTED ABOVE, MODIFICATION WILL BE REQUIRED." Those headers are 1-1/2" primaries - good for a 305, or for a low-RPM 350. The kit doesn't include mufflers, and is relatively small crimp-bend tubing.

A simple 3" mandrel bend cat-back would flow better, route easier, and by the time you get it installed, cost less.