An 8" will suffice just fine on the street unless you are building a monster....and if you were that question wouldn't get asked <g>..

8" stuff is rapidly getting out in the aftermarket just as fast as 9" component prices are going up...but..

You can still get a 9" housing with axles and calipers cut to any width you want from those boys in east central Illinois (Phillips Street Rod Parts..I think)... It has GM front calipers on it (ie: no parking brake).. You could probably get a discount for getting it with no calipers and add Caddy Eldo.Buick Riv/Olds Toro calipers that have parking brake stuff built in.

9" housings aren't too awful bad....if you shop right.
(type 9" Ford on Eaby and hold on..)

An Auburn posi is a good piece..

Watch the gear vendors on selecting your gears.
Drag race gears are softer (to absorb initial launch impact stresses) and are not as durable as street gears.

I probably spent $1000 setting up my 9" what with the Moser axles and such... I could probably trim a couple hundred off of it by buying that narrowed housing with axles...

Some pics are at:
http://community.webshots.com/album/42740280aaZVkW
and
http://community.webshots.com/album/42709364fffYOh
Hope it helps.
Jeff