broken exhaust flange studs

["Campsmith, Michael" <mgc4@cdc.gov>]

In preparation for pulling the engine and transmission on my 1974 TR6 I
have broken off all four exhaust flange studs.  But I'm still having
trouble separating the headpipe from the manifold.  Any suggestions on
how to get the two apart without trashing the manifold?  And once I have
it apart will I have to drill out the broken studs and re-tap for new
studs, or can I just use through bolts instead?

Many thanks for your advice.

Michael Campsmith
1974 TR6 about to be in a million pieces