Appart from whats been mentioned

Seatbelts if you are upgrading to retractable belts as I did the engineer will tell you how they are to be fitted.

Aftermarket seats. I got a problem with this at the moment as I hace lowered the oroginal rails in the coupe with new mounts welded to the floor. Engineer dont like this and working towards solution at the moment.

Location of fuel system components, for example I was not alowed to fit a fuel filter under the bonnet. Yes trivial this one.

Show him or discuss engine and trans mount. Mine had a specific way to do gearbox mount and strengthening the floor pan.

Any holes you want to cut. eg intercooler.