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Hey sorry for the delay, I've been out of town and have had a lot of issues to tend to lately.
My recent use of copper in my 1966 Sea Skiff repower project used hard copper pipe that could not be bent, so I used fittings to accommplish what I needed, and the fittings were roughed up with sandpaper, flux was used, and they were sealed with sliver solder, with a safety screw of stainless steel put in to be sure they never moved out of place. I found the physical dimensions of copper available today does not match up with the dimensions Chris-Craft used in the past, so be careful if you are planning on using chrome hardware around the copper pipe at the transom because the new stuff may not fit with the old hardware. You could always use a section of exhaust hose to transition from one size to another if it was a close match.
It is my understanding that K,L,M, ACR & DWV are available in hard. K,L & ACR are available in soft.
Since the original copper exhaust on a v-drive boat is actually bent with a big curve, exiting the motor toward the front of the boat and then curving back to exit out the transom, I would think "soft" would be the best choice if you were going to have someone put a curve in one for you. The designations also have to do with thickness of the pipe, and I would probably go on the heavy side if it were me.
Good luck on that, let us know if you need any details.