looking to find specs on 340-X heads.

I won't argue the point of what yrs. used what heads because I haven't had enough different ones to know. But according to my "Small Block A Engines" manual from Mopar the 894 X head was used from 68-71 on 340's. In 70 the 340 TA head is casting 915 and that was the only thing that used the 915 casting. In 71 only the 360 got the 915 head (small valve). It says it wasn't until 72 that the 340 got the 915 head.

Here's the page from the Mopar Perf. book. Sorry it's kinda blurry. Scanning from a book is hard to get a clear pix.