Chester's last Gorilla was the Western Lowland male 'Jason' who was later sent to Bristol. The last place I saw him at Chester was on the(now obscured) island the Bornean orang male 'Tuan' uses. He may have been back here before he left though.
Yes there were two grassy islands, not very large with hardly anything to climb on. The inside enclosures were what is now the hornbill aviaries. There are probably pictures somewhere on here. I remember seeing them when I was little (early - mid 80s).