As mentioned before your best bet would be dealing with either EGGE Machine and/or KANTER Auto. With my first OHC build many years ago I bought the pistons from EGGE back then they offered .60 so I would check with them first.
Also whenever I have a head re-worked I always have Bronze Guides installed,
I would think this is needed to address your stem issue.
I will also add that VITON seals are great for these engines.
Cheers.
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When I die, I want to go peacefully like my grandfather did, in his sleep.
Not screaming like the passengers in his car. 
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