I though about selling..now im thinking of cloning it.

I too thought the '75-76 Duster with a 360 was a single exhaust with a catalytic converter.

But after a long discussion on air pumps on a Little Red Express and EH1/E58 motor specs and looking at the dealer info from '75-76 I am convinced that the Duster got the same motor as the '74. No idea on what manifolds it used, but it was definitely a dual exhaust and didn't have cats. And I don't think it was available in CA, they were a Federal option only.

Personally, I prefer the '74-76 A-Bodies with the caveat that a '75-76 might fall under some emissions blankets that I don't want to deal with since cats hit around that time. I am building a '73 and wish it was a '74 due to the 3 point seatbelts and fender braces. Not impossible to add, but nice to start with both. Either way, I like the later cars for those options.

Not to say I don't like the '70-72, my favorite body style is the '70-71 Duster. But I like the later Duster body style enough that if I went looking for one I would try and find a '74 without the crash bumpers rather than find a '70-72 and add the seatbelts and fender braces.

That said, I think the OP needs to keep the car the way it is and either sell it or fix it. It is rare with the E58 option and even with the non-stock parts it will go up in value. Maybe not to the same level as a '71 340 Duster, but more than a '76 Duster with a slant 6 regardless of the numbers matching motor or not.