mike
If you pull the engine to look at the clutch, make sure the clutch plate is installed in the correct direction. As i recall, if the clutch plate is installed backwards (which could otherwise be forwards) there is interference with the flywheel.
I suspect i've got the same clutch and gear box as you in my birkin and am currently over 7K street miles without any clutch issues (yet).
my sympathies for your unintended build.
Paul.