From the rules:
A.The STX class expands the vehicle eligibility limits beyond those specified for STS,
and adds a limited number of allowed modifi-cations.
The allowances are as follows:
6.High flow catalytic converters are allowed, but must attachwithin six inches of the original unit.
Multiple catalytic con-verters may be replaced by a single unit.
The inlet of thesingle replacement converter may be located no furtherdownstream than 6" along the piping flow path from theoriginal exit of the final OE converter
IOW, a CAT delete is not allowed in STX.
But, you do bring up a good point, in relation to your local emission laws.
However, SCCA couldn't care less:
Engine and transmission must remain unmodified, including emissions equipment, except as noted below: