Note that the casting number is the same as early 360 heads - 915. Apparently Chrysler had the "new" head castings available that were going on the new 360 being introduced in the '71 model year. (360 blocks started to be cast in 1970.) So they machined the raw head castings for the respective applications - 340-6. 340-4 and 360-2. (i.e.: pushrod location and valve size) The rest of the casting, including ports, remained the same.
To me it looks like the chambers may have been polished a bit too, and valves look like aftermarket stainless. Probably "nail-head", which is better for the intakes than OEM "tulip" style.
