Bolt on spacers are not illegal - since when are they?
They will pass an engineers far as i am aware as long as they locate.
I drive my 350rwkw GTR with spacers, there is NO issue what so ever.
The car has done over 10 track days, DECA/Motorkhana's etc etc before i owned it abd has been fine for 2 years possibly longer.
They are being used on factory R33 GTR wheels to fill the guards/better track, so its not about buying "better" fitting wheels, its making them fit fine and safely
I had Police defect me the other day for tyres, and had a good look @ the whole wheel setup and said nothing.
(they were wrong, the tyres i have are actually legal, but meh, no point arguing when there was no fine/RWC involved and an officer thats clearly uneducated)