sorry if this hasn't been covered in this post already but I've not read it all:
Barnes: don't knob about lightening a LET pot type flywheel get an early xe flat type one cos it is lighteer to start with, and then get that lightened, then get a clutch from Gavin that will fit it - you shouldn't have too much trouble in this, but (off the top of my head - correct me if I'm wrong) it requires an XE pressure plate with an F28 fitting friction plate.
As for you having an XE engine:
we all know that fundementally the xe & let are the same, infact Arno's phase 5, 4x4 mk1 astra uses an xe block, so you're in good company.
I'll PM you tomorrow about the clocks. Cheers,