Until just a few years ago it was impossible to register any type of "assembled vehicle" on Oahu, while on the other islands it was never an issue. All though I'm not sure exactly what procedure you follow on the Big Island (Maui, Kaui), it's really easy. Some of the guys had their Cobra's registered as a 1965 "Ford", others as a 1965 Cobra, straight up, just like it was a real and original car. I'd be concerned about auto insurance issues myself and would want it clear on the title and to the insurance company exactly what I had.
On Oahu, the car gets a special inspection at only one location that checks for things like a DOT approved windshield, tail lights, etc., piece of cake. A special Hawaii sticker, which contains a Hawaii assigned VIN, is placed somewhere within the vehicle. The VIN assigned is the same number the car already has for a VIN, unless it's a totally new car with only an MSO from the manufacturer, then Hawaii will assign one from scratch. The title shows the MAKE as a Cobra, the TYPE as a STRD-RPLC (street rod replica), the year model as a 1965.
For many years those few of us (5 or 6) who owned Cobra's typically had them registered on one of the other islands in Aunties name, or who ever.
The Oahu cops were onto us, but they looked the other way. It was never an issue for any of us, all though, we kept a pretty low profile. It was nice to "come out of the closet", so to speak, when the registration law was changed for Oahu. Because we were under the table, rebels if you would, risky business types, only the hardest of the hardcore dared to own a Cobra on Oahu. We were a tight group, it was a special time, very close friendships that continue to this day. "We" worked hard to get the law changed, it was quite fascinating watching the wheels of legislation turning (slowly).
So if you ever sell/move the vehicle to Oahu, there is zero problem with getting it registered there.