found HJ with 18X trim

[Absinth]

this 18X is different to 18V, the 18X is a different fabric, its velour in black so it appears on this statesman

Adam, the HJ catalogue lists

Kingswood
18V -- vinyl
18X -- vinyl and cloth
18Y -- vinyl and cloth

Monaro, Premier, Deville, Caprice
18V -- vinyl
18X -- vinyl and cloth
18Y -- vinyl and cloth
18Z -- vinyl and cloth

I haven't found anything to confirm if the letter codes correspond to a particular cloth style, it doesn't seem to.

Caprice had velour trim but black would be a rare trim colour in Caprice.