The valves are NOT adjustable on the 3.2V6 SOHC
but ARE adjustable on the 3.2V6 DOHC.

Both engines are designated 6VD1.

Assuming that your vehicle hasn't had an engine swap, check the VIN Plate:

(Source: http://www.zitog.com/xr-001.shtml)

RLU = 6VD1 SOHC engine
RLV = 6VD1 DOHC engine

Aussie 1997 3.2V6 SOHC 6VD1 Holden Jackaroo SE (Isuzu Trooper/Bighorn/Monterey) 5-speed manual, rear LSD, front Lokka (manual free-wheel hubs).