Viking,
sorry, but why would that tiny gap have any significance?
If the secondary butterfly isn't sealing properly at tickover, any 'false air' which leaks through it has a much more direct path into the intake manifold.

Citroen never fitted paper gaskets when the cars were new, either between the carburettor and the insulator block or between the block and the manifold.
As long as the base of the carburettor isn't warped (because the nuts have been overtightened) and the block is in good condition, extra gaskets are not necessary.
Also, a warped carburettor base can soon be sorted with a good file and some careful work...

ken