Serial number may be R-5108B as taken from the title if it was a California
car.  For some (unknown) reason California assigned "B" suffixes to at least
some Avantis.  I have owned two that had this mystery "B".
The seller didn't help things by classifying the listing "eBay Motors >
Parts & Accessories > Collector Car & Truck Parts > Other Parts".  The car
itself has the wrong steering wheel, air cleaner, mirror(s), seat and dash
color plus no ignition shielding, etc.
Paul Johnson