Dosent work like that her in ca, if it wasn't non OPed u have to pay the back fees unless the truck fell out of registration, Wich means you have to re title the car. BUT! that takes 7 yeas so it seems like ur shit out of luck
Your best bet is to go down to DMV and ask what the back reg costs. Once you get that you can submit a form asking them to lower the fees.
My buddy bought a f350 to build a crawler from a junk yard an it hadn't been registered in like 3-4 years and the fees were like 500$, he did what I just explained and at first he said fine, il just register it A's a ohv and then they said oh wait we can help you and dropped the fees to 240$ so he got current reg on the truck.
It's just a pain in the ass because CA DMV makes u jump threw hoops, if u need any help or have any questions let me know, I have spent more time in/with DMV then I'd like to mention hahaha.