Ola
As far as I know only the 440 headpipes had the resonator welded. In the past I have owned several NOS 383 and one side NOS 340 headpipe and neither had the resonator attached.
Of course the ones I had were NOS and not assembly line. Parts books indicate otherwise, but I know of and have seen an original exhaust 340 Cuda and the resonator is clamped on it.