Modifying headers, what size collector should I use???

71 Dart.
Total new rebuild, motor dynode at 508hp@5700 and 565ft, tq @3600
So I finally got my 440 mounted in the car earlier this week. The car was an automatic before. As it turns out the driver’s side shorty header ends up coming out right at the Z-bar linkage and then pointing right at the clutch fork. I was going to modify the Z-bar but this wouldn't fix the clutch fork issue.
So the easier fix I believe other than buying new headers is to take the car and headers to the custom header shop. He says it shouldn't take him long to just cut the bottom section off the headers and re-route the pipe to miss all the 4-speed linkage and clutch.
My question is I guess is 2 parts.
1- what size collector should I get him to weld on to the end since I can make it any size I want now that it is getting cut? Original size is 2 1/4". I want the car to sound great and I know it will, but not so loud I don't want to drive it. I don't have pipes or mufflers so anything goes really at this point.
2- I am going to get him to change the passenger side collector at the same time even though it fits fine with no obstructions. Question Should I get him to make this side the same length as the driver’s side if he has to add a bunch of length and come out at the same location as the driver’s side even though it fits fine now?

It's long winded but I hope I cleared up all the variables. Doubt it though you guys are incredible thorough on here when you want to be.

Thanks
Butch