Floor pan replacement on TR6

I am a beginner and this will be my first fame up restoration. I have the body ready to be lifted but I need understand the process of replacing the drivers side floor pan. I assume I need to replace the pan before lifting the body. The question I have is how hard is it to cut out the old and how do you replace with new. I was hoping it would be just a bolt process but it looks like the pan is a welded unit? Any website as to the how to DYI ?