First thing I'd do is sell the rhino case. Although they look strong, all the extra re-inforcing ribs are in the wrong places. Note that they are above where the 4 gears are. A regular trans case will never break there. Note the extra ribs are not very big under the diff. That's where extra strength is needed since that's where they break in drag cars. Also, the rhino case uses the smaller weakest pinion bearing. And you are stuck with the early throw out bearing. If you go to the drag racing events you won't see anyone using a rhino case. You'll see stock cases gusseted.
I think you are better off getting a 71-73 IRS trans and converting it to swing. You get the larger pinion bearing, guided throw out bearing, and bigger clutch cross shaft. Then get a SSC core for the 9 tooth mainshaft and shifter parts. Buy late 002 gears from ERCO with the syncro hub already welded on. A chromoly pinion nut. A superdiff.
I recommend a 4.12. Its just a little bit better driving in town, and gets you out of the hole better. Go with Geoff's gears. Unless you think your trap speed will be higher, then you'd need a taller 4th.