Well this is getting away from the street car purpose the original poster was following...

I was at another builders shop a few weeks ago, and he had an engine on a stand that used valves with teeny stems... looked by eye to be about 3/16 dia probably less , and "bee-hive" springs....of course with these valves you need custom guides...

Beehive

This is getting into the really custom realm though....

I havent used the company Henry mentions, but I will check them out. We send alot of cranks to Armondo, and he can either repair the crank the stock dimensions(which save mucho headaches), or resize the journals if you so wish...

On a street application I'd opt to repair the journal and go with all the stock internals.