i have a 68 firebird...the interior floors and trunk floor are extremely rusty ....completely un-repairable.....how difficult is the job of replacing them and is there a instruction step by step manual ?  

My 70 Firebird is almost the same way, just a few rusty holes on the trunk and interior floors.  What I did was I had a friend hook me up with some plain sheet metal and when I go to install it, i'm just going to roll it into shape and weld it in (you can pop-rivet it but I don't recommend this process). If that sounds tricky, National Parts Depot and Year One have catalogs where you can order the pre-molded interior and truck floors. I'm pretty sure they will have some sort of installation instructions if you order the parts. If you do it yourself, your probably going to be doing a lot of cutting away and removing as much rust as possible. After you install them, you have to put this stuff on it (forgot what it was called) that will keep it from getting rusted. I hope this information helps lol  

Guys, the Jan 08 issue of Musclecar Review (sorry HPP)has a good article about changing the trunk floor in a Plymouth GTX, that shows most of the steps to do this. It can be a lot of work but most of this stuff is available in repro parts, so it can end up looking factory stock if you're careful.  

The important thing about full length floor pan replacement is to measure and mark all four corners of the seat pan or your seat will not sit level.The sub-frame bolt, bolts to the seat pan and will help get it in the right position, but you still need to level it. If the area under the seat pan is good just replacing the front and/or rear floor in sections is best the seat pan has alot of hidden spot welds.