When looking at 12 bolt posi rear ends for first gen the $1800 to $2500 I see regularly is out of my range. The beauty is that the center section from a full size 69/70 has no ears so modifying one will be more reasonable and will look factory stock.

I have a jig for just that purpose! centre section from the full size and tubes out of a camaro (8.2)10 bolt and you are there.