I've got a 69 Malibu that I'm getting ready to drop in the new crate motor soon, it should be sitting right at about 400HP..... I'm worried about tearing the stock rear end out of it and really hate the idea of a non-posi. There is a nice unit listed on Ebay if you do a search for a "69 Chevelle" for around $600.... Is there anything that I need to look at to make sure this thing will work? I'd hate to go get this thing and then find out it won't work

You could build the rear end that is in it now. Post a link to the other rear end so I can see what you are looking at.

http://cgi.ebay.com/ebaymotors/68-69-70-71-72-Chevelle-12-Bolt-Posi_W0QQcmdZViewItemQQcategoryZ33731QQihZ010QQite mZ200012421647QQrdZ1

Well, other than the Auburn it seems all right. Are you sure that you want 4.11 gears? I'd replace those ratty brake lines with some reproduction lines. Ask if all of the brackets are in good condition. Sometimes the lower part of the shock mounts are broke off from using air shocks.

so what do you think I could get away with money wise turning my 10 bolt 1 wheel wonder into a nice posi??

If you don't change anything else, the posi with new bearings and shims to set the backlash will cost $512 plus shiping, and your labor to install it. If you change the gear ratio too then you are looking at more money for parts and labor.