Catalytic converters

When I bought this car the old exhaust system was falling apart. One day it decided to fall on me and took everything down with it including all four stock catalytic converters. They were all clogged from the hard drop and from being drug on the road until I could find a spot to pull over. Fast forward to now, I currently have aftermarket headers, a catless H pipe on there with a Borla catback exhaust (so it has a GT exhaust conversion). I purchased two high flow catalytic converters to be put on so it will be street legal because in Missouri it currently is not. When I brought it up to the exhaust shop I wanted to do my install, he told me I needed the pre-cats as well for it to be legal. I personally thought you only need the two main catalytic converters for it to be legal but this guy told me otherwise. So I am not sure what to do because I am not sure if this is true because I have not been able to find anything about the amount of catalytic converters you need for it to be legal in Missouri (I could only find that clogged catalytic converters can be placed with OEM ones of high flow ones), nor can I find pre-cats anywhere. Could someone please help me?