Far and away a short block because a lot of guys have their own worked heads. A forged sb is a hot item imo.

 

Thompson sells a forged 408 iron short block for $4700 with a warranty. People wont be as likely to spend that much from an individual. So around 3500-4k tops.

Heads, you can get brand new GMPP ported LS3 heads for 1500 and stock for 1150. Yours being used and again not new with warranty, but have over sized valves.. maybe 700 ish?

Add in lifters, cam, coils, valve covers, around 1500 - 1800

Starting at 5500-6k doesn't seem to bad. You'll end up taking less.

Those are shoot from the hip and you don't state how much of it is new or used (cam, springs, etc)

You may get more by splitting it up.