The event that I'm worried about is Hill Climbs and the tech inspections for those are usually pretty thorough.You can fit most anything into these cars if you are willing to massage the trans tunnel. And by massage I mean sledge hammer and meaty fists.
To get low you will need to mount the seat up with your own brackets/handiwork and experiment with seat padding arrangements. To get even lower look up about cutting the factory floor seat mounting positions out and bolting the seat directly to the floor board of the cockpit.
In my experience autocross' here in the NW don't pay too much attention to the broomstick tests. Track days.. only marginally more so. Keep that soft top up and suck it in if they do ask.