Valiant surgery 2. Before I cut

Yea, I completely understand the intimidation factor.

In my opinion (please confirm), I do not think you have the support brackets circled in the first and second photo. Even if you do, I doubt you will get all the way up into them with your cutting. True, you will need to drill out the spot welds, but you can probably leave all of the bracketry, and then trim them down so they fit exactly to the new tub.

This was why I joked about becoming intimate with your tape measure, your grinder and welder.

The reason i suggest the full tub is that you will be time ahead by starting this way. You have to do a lot of measuring to the tub to make it fit perfectly, but I still think that is the easiest way to do the job you are proposing. There is no doubt in my mind that you can make it work with the inside of your factory wheel tub, but I think it will be cleaner and more functional with the method I am describing.

Like I mentioned before, this sounds like fun. It is much more involved than my project, but sounds fun.

Thanks,
OldMoparsRule!