Hi Nick,
For wing mirrors, Car Builder Solutions do a range that are IVA OK. I bought a cheap set that passed but the glass was poor. Have now bought an expensive convex Motorsport set from Demon Tweaks which are very good. I reckon good rear vision is an essential. I also had a set of bullet style race mirrors but they were not good either.
For headrests, I fabricated a rectangular aluminium back plate (bolted to the roll cage at head height) and had it padded and trimmed in leather
My front indicators are located in the lower driving lamp recess and you will need side repeaters visible from the rear three quarter
You will need to source wheel nuts to suit your hubs and wheels
Hope this helps
Cheers
Roger