1970 340 Duster rare x car.

Since I own 3 70 340 cars... thanks for the compliment.

340 cars in 1970 could have had X J O U Z heads. The X heads ran out about mid year as supplies were bled off from prior year run 1969. I have one car that has X heads, another with J heads and a 3rd with an X on one side and J on the other. Go figure. the X head cars were built in early dec 1969 and before.

Having X heads on a 1970 model year car isn't rare or unusual at all.

Your story is full of holes has some serious misinformation in it and NO car off the assembly line in 1970 had an electronic ignition in it. PERIOD. What's the date code on your distributor tag, or is that missing as well? :)
BTW without the fender tag or broadcast sheet you can't say it has ANY rare trim package, because you don't have even one shred of valid documentation to support it. I have a 70 Duster out back that came with a 426 hemi, factory installed, I promise... trust me just like Joe Isuzu. LOL

Puffing 101