If the system I think it is, two things.
There are plugs underneath the exhaust manifold held in by a small bracket and a 10mm hex nut. 4 of them. There is a genuine plug for the holes and use new gaskets. I have heard a 10c coin will also work, though the plugs would be much better.
There will also probably be a large screw in fitting somewhere on the manifold, about an 18mm thread. That one needs to be plugged too. I forget where that plug came from (a couple of years ago).
I think there is a pack of gaskets in the workshop somewhere, they come in a bag of 4, so if you order 4 of them you have spares.
Pretty sure @carnut222 has done this more recently, some of those spare gaskets went to his workshop.
May be useful to check the firewall for leaks, you really should not smell anything in the cabin. The exhaust is on the other side too.