No Bronze Guides, Any Reason?

My .02.......

The factory iron guides are fine for the softly sprung low lift factory cams when used in conjunction with the OE style seals, that don’t seal all that well, along with the actual factory guide clearances(usually .002+ on these old mopars)....... not to mention from a manufacturing standpoint...... it’s cheap to just drill a hole in the iron.

Step up with more lift, higher spring loads, seals that allow less oil to pass by, and the desire to run less clearance to maintain the integrity of the freshly done narrow valve seat........ and iron becomes a less than optimum choice.