Duramax lb7 R&R

I have a 2003 and a 2004 Chevy Silverado with lb7s in them. The 2003 was overdosed on starting fluid and the 2004 has a ton of blow by and it's getting a little noisy I am looking to replace both Motors and I would like some suggestions of the best way to do that economically. I would prefer to just Exchange Motors complete if possible anybody have any suggestions thank you.