This looks to me like the two hybrids 'Rajang' (from Chester,who is still there) and female 'Annie' (from Brookfield zoo, USA). After 'Annie' died she was replaced with the Sumatran female 'Djambi from Twycross but the darker coloration of the female here makes me think its Annie.. However I am not sure if her date of death would fit with this.
'Djambi' was 'spare' from Twycross after her mate there died. She was from an over-represented line so nowhere particularly wanted her for breeding- hence she ended up where she did.
Its a pity she didn't go to form a new pure pairing somewhere else really.
This looks to me like the two hybrids 'Rajang' (from Chester,who is still there) and female 'Annie' (from Brookfield zoo, USA). After 'Annie' died she was replaced with the Sumatran female 'Djambi from Twycross but the darker coloration of the female here makes me think its Annie.. However I am not sure if her date of death would fit with this.
I think you are right about them being hybrids, and also about that awful dark enclosure, I would say that at the time, apart from the Black Crested Mangabeys cage, that ape house was the worst enclosure at the zoo back then.