hmmm! so a motorcycle with side car and one head light is ok but a 3 wheeler with two close set head lights isn't ok? or, a trike with a mc front end and two rear wheels and one head light in the center is ok but the elio is not? there is a story in the u s about a car in the '30s that had the head lights mounted on the extream outter width of the vehicle and a motorcyclist thought is was two other motorcycles riding abreast and would scare them by going between them. the outcome was predictible.
I can't answer all those questions, because I just don't know. Unfortunately, what was or wasn't allowed here in the 1930s, or even the 1990s, isn't allowed now. The rules got really tightened up here in UK in about the year 2001. Vehicles have to go to the same testing stations as heavy goods vehicles.
I have however read the MSVA (motorcycle single vehicle approval) regulations which apply to a personal import or low volume vehicle such as the Elio (unless they put it through the full type approval, which would involve crash testing etc). As far as I can tell, the headlights on the P4 probably don't comply with the regulations because they are too far from the outer edge of the vehicle. The regulation requires a maximum of 400 mm (this would be taken as the outer face of the front fender) and since they moved them to the main body shell, I'm fairly sure they are outside that.
My own home built car had to go through the same type of testing (SVA, single vehicle approval) and I was fortunate and glad that I'd looked up the regulations in advance (I bought the testers' manual) and made sure my build complied, so it passed first time out, which wasn't happening elsewhere. Some other owner/builders of the same car ended up with over two A4 sheets of fail points. If you can't get the vehicle to pass the test, it cannot be registered. It's a show stopper.
The regulations elsewhere in Europe are even stricter than in UK. For example in France, you cannot register a home built vehicle because there is no other way than full type approval. Some French owners build their vehicle, bring it to UK to get it through the testing and registration process, then export it to their home country and re-register it.