stock floor body drop

I am going to be stock flooring my 91 isuzu pickup in the next few weeks. The plan is to strip the frame and then cut the four or five inch frame rails down and insert a piece of 2x3. not sure if I need .25 wall or if .125 will work to be structually ok. also the section I will be working on under the cab has a simple bend in it. The truck already has a back half out of .125 wall 2x3 which i know needs more bracing to the original frame. I have read about this a little on the internet and from some people just want to make sure this is the best option for a low budget any tips, pros, or cons. thanks.(traditional bd is not an option)

with my 94 isuzu, when i built a stock floor frame, the 2x3 was still too tall to lay rocker. i also had a traditional body drop to get where i wanted, which was an inch from doored. you wont gain enough by using 2x3, plus adding that inside your stock frame rails. ive seen isuzu stock floored with 2x3 sideways, or 2x2 parallel rails.

did the 2x3 fit inside the stock frame rails?