"Can I beef up a Dana 35?"
no. not enough anyway. everything is "beefupable" if you will, but as Eddie said, you're still stuck with C-clip axles. you're also still stuck with the too-small ring and pinion of the D35. save your money and look for a swap candidate. a lot of ppl will say get the 8.8, and it's not necessarily a bad choice. just get the right one from an explorer, not from a ranger-they have 27 spline shafts. it's been a while since I researched 8.8's -I had one in my old MJ, but I believe the good ones from are 1996+ explorers. the only thing about the 8.8 is that it is slightly narrower than the D35 you now have, and you'll have to get a mount kit to install it in your TJ. my suggestion would be to look for a TJ D44 to swap in. that way, it is literally bolt-in, no welding required, no spacers.