Before you change anything - you are going to have to do some pre-work to make sure you don't have issues down the road
- If it doesn't have the hard top on - bolt that on first to get structure to the truck
- Check all the rubber body mounts and bolts - if they are gone or rusted - you will need to replace those as well before you do anything taking note of where the factory shims are at each body mount. Top and body mounts will get you in a way better spot before you start cutting.
- With top and new body mounts - check the doors to make sure they open/close as they should without sticking - shim as needed
- Once I had everything lined up and took measurements at a few key spots (windshield frame to bedside, etc.). I then took the top back off and re-measured to confirm my gaps had not changed.
- You don't have to remove the rear bedsides if you don't have to - the cargo floor is bolted in with tack welds in a few spots near the tailgate. A handful of people have cut out the old cargo floor, spread the rear quarters and slid in the new floor with an extra set of hands. The B-pillar metal has enough flex to do this w/o damaging the quarter.
- The torsion boxes (rocker boxes you refer to) bolt in at the B-pillar to hold the cargo floor in place, and then are welded in at the front at the firewall - this piece is the key structural part of the blazer when the top is off. I'll imagine you will have some other parts needing replaced under there once you dig in a bit. The ones on the truck I repaired were solid so they helped keep the truck aligned with the top off.
The line that tells people to fix a panel or replace a panel - is all over the place. Some will say - ' keep as much original metal as possible' others will say that 'it's easier to just swap in a new panel' - it really comes down to your talent, patience and budget.
I just swapped the entire back half of a blazer over a few weeks this past summer. It was very educational to see how these things are built and to note where rust is hiding. I took measurements from the old bedsides and then drilled equivalent holes in the new bedsides and put the top back on without any issues and the doors open/shut like they did before.
Rocker box is not the same as inner rocker. The inner rocker is an extension of the cab floor and is usually rusted out if your floors/rockers are rusted.
Going back together order that I used:
support brackets for floor/rocker (torsion) boxes
rear cargo floor
wheel tubs
bedsides
outer rocker - this will take some time to adjust before the doors line up so don't finish weld this piece in until you confirm you are lined up.
Get some pix of the truck and several on here can tell you what you are going up against.
Here are a few helpful links to get you started.
Door Frame Measurement links - check these before you cut anything - especially
this post.
Parts list I shared with another board member when he was building a blazer.
Build posts have a wealth of knowledge and in the past few years, the aftermarket panels have surfaced making this job a bit easier.