'75 318 exhaust help

I want to add dual exhaust to my '75 318 Scamp Brougham. I found a system from TTI but I am unsure about my casting numbers on my current manifolds. I am going to take them off and check them soon. I've been looking on e-bay at 340 manifolds. According to the posted 340 casting numbers on this page, if I'm correct, there are only two numbers to look for on each side.
Drivers