Yeah, The Flex-Pipe Doesn't Work...

Dana67Dart said
IMHO

You might have better exhaust performance with a properly sized single exhaust than a dual on the 2bbl.
From AccurateLTD.com (Accurate Exhaust) website for A Bodies. Note pipe sizes, the Y pipe is the same for all (I BELIEVE) since you are only putting 1/2 of the flow through each side of the pipe.
Click to expand...

The "Y" pipes are very different, the HP "Y" ends in a 2.5 in pipe while the std 273 "Y" ends in 1 7/8 ?, and you can only look at 64-66 A body Plymouths. The width and the drivers side exhaust manifold is different than later cars. Flex pipe is also horrible for flow.