These showed up yesterday.

A little review:
The Castor Cup Racing Series was a JAF sanctioned, one marque race, for Isuzu Gemini cars. The series was run by the Isuzu Sports Car Club and the series ran from 1979 through 1993, spanning all three generations of Geminis. The series had at least 5 races every year, and some years may have had as many as 12 race weekends and championship runoff events in addition to those 12.

The descriptions say these videos are from about 1990. Probably they are actually 1988 or 1989, because there are no third generation cars.
What is surprising is the mix of the first and second generation cars on the track at the same time, and if the notes are correct, racing against each other in the same class. The first generation cars are PF50 and PF60, RWD, double wishbone front and beam axle rear suspension, running as much as 130 HP from 1.8 liter DOHC 8 valve NA engines. These would give an AE86 a run for its money. The second generation cars are the JT150 and JT190, with strut front suspension and beam axle rear suspension running 120 HP 1.5 liter SOHC 12 valve turbocharged engine or 135 HP 1.6 liter DOHC 16 valve NA engine. The latter was Isuzu's answer to the CRX Si. I would not have expected these two types of cars to be able to coexist on the race track, but the FWD cars look to be holding their own quite well.

Looking at the videos, for an event made up of enthusiasts of the cars, they are not afraid of trading paint. Winning seems a lot more important than keeping the car in perfect condition. A few drivers seem to be ignoring the rule that unless the passing car gets along side before entering the turn, he is supposed to back off. One of them appears to be depending totally on laying his fender into whoever he is next to, in order to guide him through the turn. And if the last video was shot after the race, the other drivers do not appear to be lynching that driver.

Class 1

Class 2

Pit area