There was mention on this forum a while back of a difference between HD and HR control arm length that had an effect on wheel alignment but not sure whether it referred to upper or lower control arms ( I think it was lower from memory
) or how correct the info was.I remember writing down the info on the differences at the time but can't bloody find it now.
Anyway,if you don't have any luck here,
A mate of mine got a lower control arm from Classic Oz Wreck at Toronto NSW ph 02 49594546 or 02 49598999 a while back ( it wasn't cheap ) they might have what you need.
Maybe try also A and B Holden wreckers in QLD ph 07 3808 1678.I recently bought some parts from him and he seemed like a nice bloke to deal with and the price of the parts I bought wasn't too unreasonable.
Here's some other numbers for early Holden wreckers I got from Just Parts magazine.
Harrisons early spares 07 3801 1986
Auto wreckers Geelong 03 5278 8031
Holdent 03 9544 9155
Hope this is of some help.