Regarding engineering you'll have issues with the following:
Vented Bonnet (especially if fibreglass and not ADR approved.)
Carbon Fibre Mirrors (Same deal, if not ADR approved)
Race Seat (Again, issues if not ADR approved)
Gauges (depending on placement)
These are particularly difficult due to the costs involved for the tests if they are not ADR as you'll have to foot the bill proving these meet the ADR requirements, whether they pass or fail.
ECU, turbo, etc is fine if you pass an IM240 test.
Oil cooler should be fine.
BOV is fine if it doesn't vent to atmosphere.
Front Facing Plenum I would have no idea on (this might come under IM240 and review of piping placement)
Airbox - as long as it is covered. Can be a sticking point as some may say it needs to be covered when the bonnet is open, others is fine if it's enclosed with bonnet closed.
I am not an engineer but I have done a lot of research into RMS Engineering, the ADRs and talks with engineers on testing requirements, process, etc.
Hope the info helps.