X2 on the idea that you need a better machinist. I've seen premature guide wear caused by too-efficient valve stem seals, especially if positive stem seals were added to what was already there, such as the O rings in the groove under the split locks. Rather than replace the guides, try to find someone who will ream them out and install bronze guide liners. The liners are available on Ebay, and it's a fairly simple procedure to ream the guides .030" oversize and install the thinwall liners, then ream the liners to the proper oil clearance. The bronze lasts much longer than the original cast iron, especially if they're clearanced properly and used with the right design of oil seals.
Jerry
