After we learned about the interior variation on the Flying Customs Nissan Skyline, we reached out to Mattel Project Designer Steve Vandervate, who has a hand in many of Hot Wheels’ premium and collector lines.
The Basic tool set was modified for use in Flying Customs, adding a DC chassis and single-seat interior. It appears that the Flying Customs pieces that are using the stock interior must have been early-runs that used the basic tool set interior piece, and this was corrected as a running change. There were no plans for a roll cage – if there were, it would have been a live hinge on the interior piece.
Per tool plans:
Nissan Skyline 2000GT-R #X0092 – Basic tool set, ABS chassis, stock right-hand drive interior.
Nissan Skyline 2000GT-R #X8219 – Flying Customs tool set, DC chassis, single-seat right-hand drive interior.
(Trying to find it? Here are all the listings. Hard to tell what is what, but I am sure you can ask the sellers…)