Some earlier AMC heads had improperly hardened valve stem keepers that
failed with disastrous consequences.  According to my rebuilder, this is
no longer a problem, and he guarantees them 12 mos/12,000 miles as part
of the engine.  I inspected mine closely and they certainly look good as
far as the casting and machining goes.  You can't tell about the
metallurgy however, but that is not rocket science either.  We have to
trust that they are good quality, I don't think there are any other
sources.

 Consider the 3-angle valve grind too, shouldn't cost more than $35 for
both heads.  With production heads you get 45 degrees +/-, the three
angle will seal better and longer.
--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia w/2.1
'65 MGB (Driven since 1969)
'74 MGB GT (Restoring)

Assisting on Restoration:
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Parts cars:
'68 & '73 MGB, '67 MGB GT