Welcome to Hybrid Vince. You have found a wealth of information on your car here. All of your questions have been asked and answered many times before. I'll offer you some of my insites but I strongly recommend you devote a few hours to the search function. One thread is just inadiquate to give you enough info to make good decisions.
First off, I would suggest you install an overdrive tranny instead of the th350. The rear gear ratios available to you are too high for comfortable highway speeds. 700r4, 200r4, 4l60, or manuals, T5, T56.
Roll cage and strut bars will likely provide all the reinforcing you'll need. Many guys here have fabbed frame connectors and found that that is all they need.
Rearends are a big subject here and you really need to do your homework on this one (read "search function"). Basic overview: 240's, 260's, 280's, had R180's, good to about 250 hp. 280Z's and 280ZX's had R200's, good to 400hp. Both are open diff's, but in an IRS (independant rear suspension) wheel loading is near equal so one-wheel burnouts are rare. There are other reasons for wanting an LDS though so I won't presume. LSD's were available on special models on 280ZX's and 300ZX's and are hard to find and/or spendy. The R200 LSD is basicly a bolt in. The later R230 LSD is a much more involved swap. Don't make a decision based on this. There are other issues to consider back there as well such as u-joints and CV-joints.
Read, read, read. Also, are you going Scarab, JTR, or MSA? If can't answer that you need to back up and figure out what that means first before you address these other questions.
Glad to have you onboard. 8)