Only one of my 10 Novas(that I've owned) that ever came loose was my first 70 Nova that was all stock 307 and stock bolts. Last two Novas/converters are threaded Freakshow converters.They are threaded, I just always made sure I used a bolt long enough to nit the backside. I always used a lock nut also.. never wanted them to come loose and that was just extra insurance.
My OCD kicked in and I did it again on my LSx build.