Dual Exhaust Conversion

They are very nice. Very expensive! BUT! IMO, there name say it all. Top notch restoration exhaust stuff. My question is, do they do oversized pipes? The stock exhaust pipe size is small. An upsizing would be helpful in power and mileage. I do realize that just doubling the exhaust pipe is a nice help. Increasing both the pipe sizes would be better. Not mandatory though.
For Accurite it looks like stock sized pipes. They do require exhaust manifold numbers though. Their system's do fit right. TTI if you want larger pipes.