There is no such thing as a base model Monaro 4 door. The sedan versions were only ever GTS models and were initially a special vehicle package code XV4 on a HQ Kingswood sedan. Then from HJ-HX they were plated as a Monaro GTS sedan and just GTS sedan for HZ.

That car listed above is an L31 optioned Kingswood sedan, it isn't an XV4. If it was an XV4 it'd have 30X or 30Y trim not 30E. What it is, is someone wanted a 308 powered HQ sedan and probably was smart enough to realise that optioning L31 (308) on a HQ V8 Kingswood sedan was far cheaper to insure than any XV4. I wouldn't be surprised if it also had U21 dash and N66 rally rims. It had no other mechanical options other than L31, so it was bog standard mechanically other than the 308 engine optioned over the standard 253. The BODY tag read L31 M21 GV2 (308, 4spd and 3.36 rear axle).

It was sold by possibly Commonwealth Motors in the ACT but you'd need confirmation on that.