Kid here's a option on valves if you can contact the seller in his description of the valve train parts the valves listed are 8mm stem at 1.715 also it state special order valves available
Alt URL:
http://www.ebay.com/itm/MOPAR-170-198-225-SLANT-SIX-PERFORMANCE-VALVE-TRAIN-/300707967270
As for the article memike I believe the early casting heads are less desirable. But honestly I'm new to the slant world and only taking this info from what I've read I believe it say pretty much the same thing in the 6cyl mopar performance book as well
Hope this helps
Aaron