I learned awhile back that there are two different sizes of valve stems in my "D3DE" 250ci head on the OE 66 200ci shortblock in my 66 Falcon SW. IIRC, they are 11/32" and 5/16" with 302/5.0L valve springs and one piece retainers. At what level of a build does one modify a head in such a manner? The cam is an Oregon Cam grind 268S with .440"-ish advertised lift, CI headers, and a Weber 38. I just noticed a sticky dealing with porting the Log Heads (w/table of big/small/Aussie) and was wondering where is the porting done with the log cast into the head? Thanks, RodC.
Different Size Valve Stems:
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The 289 / 302 V8 valve springs are a good swap for any small six even with a stock cam gives you a just little more revving RPM over the low seat pressure stockers. Using a smaller valve stem and tapering the valve guide in the valve bowl are ways to get better flow too, the small six can use all the help it can get to let it breath especially on the intake side. On porting intake side of head open up the carb opening depending on what carb you plan to run (ie stock type 1V, 3 x 1V's, a 2V adapter or with a 2V direct mount plate) like with most other engines opening up the valve bowls, tapering the guides, and reaching back into the port opening an blending as far as you can helps a lot. Your done at that point unless you want to open the top of the intake to gain access to top op intake ports and then make a plate to seal it again and or install multiple carbs. The exhaust is easy to open up with access from both ends. What size vales did they install in your head? Many performance builds go with a 1.750 intake and a 1.50 exhaust to help the small sixes breath. Good luck 
