Installing 408 Long Tubes, and Trans any tips?

I finally got my 408 stroker. It is a long block. I have a tko 600 trans. I plan on bolting the motor and trans together for the install. I also have accufab long tube headers that need to go on. I have installed 5.0's before, but never any long tubes. Any tips or advice? Should I lay the headers in the engine bay first and then drop the motor and trans in?

I got everything in. Very tight fit but everything looks great. It wasnt easy putting the headers in. I had to jack the motor, twist it lower it, etc, but it was worth it.