Here are a few Engine sources to look at. I only have experience with Spaulding Automotive. I will elaborate more when I finally start my build thread.
SPAULDING AUTO
Here is a you tube link from one of their ads
Spaulding auto ready to run package
A couple people have bought from these guys
Schram auto
Pacific fab also does pull out and ready to run packages they also have a pretty cool 4X4 Ls crossmember I'll talk about later
Pacific Fab
Another vender that seems to have happy customers?
TNScrambler
And last but not least car part.com
Car Part.com
These are all just a reference, buyer beware and I am not recomending anyone at the moment. Ask questions, try local and good luck there are deal out there