8 3/4 Identify & value

Hello, I found a 8 3/4 locally; although I am not familiar with them.
Heres ad:

I have a rear end out of a 67 belvedere, it is a 8 3/4, not froze up. not a posi or L/S it is a open spool with 2. something gears in it,good rear end. $150.00, It is a 489 cas. thanks paul, duster/dart parts avalible too

Is this too wide for the Duster?

What is the going price for these? Is it a good deal?

Compared to this other one:
Also have 8 3/4 A body rear end with the center cection has 355 posi unit. drum to drum small bolt pattern axels with green barings. Brand new brakes not in pics right now but will have them on tommarow. $1200 O.B.O

Large price difference.
Just wanted the experts opinions.
Thanks