No, use a proper piston to get compression unless this is a super budget build. If it is, then mill the heads.
Im not sure what the heck a down pipe is. I’m sorry, but your going to have to learn some “Old Man Lingo!”
A bigger diameter pipe will have very little in influence on sound. It’s more of the muffler. A larger diameter tube will have an effect on power by moving the power curve upwards and hurting torque down low. Size the exhaust pipe and headers for the build and driving arena you’ll be in.
The actual sound out of the exhaust pipe is due to several items in f the engine and exhaust. Again, mainly mufflers.
