All good arguments, but let's get real about things..... It's over 30 years old and had an accident that required a replacement chassis section. The rest of the ute is as it was originally.
I'd be devastated if My perfect, original Sandman ute was no longer regarded as a Sandman because a panel beater used a second hand chassis section (common practice at the time), possibly covered by an insurance claim.

The chassis should have been either re-stamped with the original number or had the new number removed and a police number stamped, but in my opinion the owner (and subsequent owners) shouldn't be penalised for an accident.