I chose to use the temporary method for now. The car is up on jackstands so it just seemed easiest
I bought two 18-inch sections for $5 each, still need two more to get them over the cross-brace that convertibles have, plus some sort of sleeve to connect the temporary pipes.
Just drive it. I drove mine open header for about an hour once. My ears were ringing for about 3, but I sure did get a lot of looks. Mostly frowns, but the kids loved it! I must admit, I live way out in the country, but I cruised thru a couple of towns. Earplugs help
I tried to finish installing my 351C a coupla years ago before I moved to my new house. I had to break in the motor the first month at the new house. Already had my mufflers but no exhaust system. Connected the mufflers to the headers using beer cans and radiator clamps. Drove it open headers to the muffler shop.