<VV> Crossover pipe inner bolt threads

[Kirby Smith]

To start the new year with a project I didn't need, I find
that the inner tapped hole for the turbo crossover pipe
attaching bolt is partly stripped on my r.h. cyl. head.
This seems to be due to
	slightly short bolts (2-inches)
	over enthusiasm by someone
	the holes are counterbored (?!)

(W.r.t. the latter point: On the heads on the car now, which
I believe to be the refurbished originals, there is a
roughly quarter-inch counterbore below the casting hole
before the threads begin.  This potentially costs me a
quarter inch of thread.  A second set of turbo heads
purchased from Bill Thomas, ca. 1967, are not so counterbored.)

Anyway, while longer bolts may be sufficient to grab
remaining threads for the 10 lb-ft of torque required, I
think tapping for an insert would be better, _if possible
without harming something_.

Thinwall inserts (e.g. Jergens, require tapping to 7/16 for
a 5/16 inner thread.  Is this known to be doable without
breaking through somewhere one shouldn't?

Thanks

kirby