Tenn HB,

Sounds logical, but you note that the Spanish fitters' trick involves making the hole after they fit the lumps in the action. Not saying it is the only way but it is the easy way.

Also, have you thought of a replaceable shoe in the hook? With such a shoe you give yourself the luxury of making mistakes, in case you do not get the fit right the first time you try again with a new shoe. In my prototype SXS I incorporated removable shoes both in the cross pin and the rear lump where the underbolt engages the lump. You can see it here
http://www.oplognosia.com/english/sideBySide.php

scroll down to the subheading barrels and see the pic.