Front floor pan replacement questions

[fireguyfire]

A couple of questions regarding replacing the front floor pans with a full AMD floor pan on my 69 project car.
The previous owner has already cut out the floor and has the AMD full pan sitting in loose which is great for me as I would rather install it myself and make sure it's done right.
The previous owner took some square tubing and tacked it in diagonally I side the door openings. These are very much in the way for when it comes time to install the new pan, so I'd like to remove them.
My understanding is that on unibody cars the strength is in the roof and the rockers, which would make these braces unnecessary; can anyone confirm that so I can pull them out?
And secondly, I'm curious what you guys and gals have done in regards to leveling up and squaring the car up before welding in the new full front pan.
A description on a suggested way to prepare for the install would be appreciated!

[Mike DC]

"The unibody gets its strength from _______" <--- It's never that simple.  Some areas are more important than others, but removing any large piece of the unibody will compromise it.  

If you've got solid subframe rails, tranny crossmember, the rocker boxes, and the connections between them are intact . . . then you probably won't get into too much trouble.   But it never hurts to brace the body with some angle or square tube.  I always do it.  If the previous owner tacked that tubing into place before he cut the old floor out then I would definitely vote to leave it there until the new floor is back in.  If that stuff is seriously in the way, then weld in some more convenient bracing of your own to replace it.  Add your new pieces in place first and then cut the old ones out. 

Frame data for collision repairs.  



I like using cheap trailer-type jackstands to help get the car sitting straight & level.  They use a big threaded rod instead of notches so you can fine-tune their heights.   Put the body on 4 real jackstands under the cabin area (they are stronger & more stable) and then add the trailer jacks farther out at the ends of the frame rails to help hold the whole thing very level.  



Make sure you have the floorpan tacked down with a few welds in many places before you start putting a lot of welds anywhere.  Especially don't start welding the sides to the rockers before you have the floor tunnel tacked to the trans crossmember.    

The most unsafe welds are not the ones that look like crap.  They are the ones that look good but didn't penetrate far enough.
           
             

[fireguyfire]

Great information Mike; I appreciate it.
The drawing makes it clear what a guy is going for; what always confuses me is when people refer to "levelling" the frame, when I fact very little of it is level; rear area under the trunk angles upwards.

Luckily having removed all Rene ants of the old floor, my frame rails and tranny crossmember are in excellent shape.
This brings up the next question.
I will be painting the bare metal spot weld flanges with weld through primer before installing the new floor pan, but what are you guys using to paint/treat the inside of the frame rails and crossmember themselves since everything is exposed right now?
I know this will open the age old debate about products like POR 15, etc but I'm wondering what you guys and gals on here are using

[Mike DC]

Inside the frame rails - epoxy primer gets my vote.  Put some weld-thru primer on the actual flange surfaces to be welded. 

POR-15 is not a crap product but it has complications that more conventional coatings don't.  Adhesion issues, topcoating with other stuff, etc.  Epoxy primer is just easier to deal with IMO.   


Be aware that weld-thru primer works but it tends to reduce weld penetration, especially if you put down a thick layer of it.  Do some experimenting with the stuff on scrap metal before setting your welder amp & wire speed settings.