I have a LS-3 , 6L80E swapped Rubicon , you really don't want the Rubi T Case . It's not necessary and Alasha is right it's just a little weaker setup .
The new trans will have approximately the same 1st gear as the low range of the Rubi Case , I have only shifted my transfer case into low range once since the swap , it was too low for the power and the trans and went through the 6 gears quick .
Everything that I had to do in low range before is now done in 4 Hi , pretty much 4.1 to 1 first gear anyway .
The 231 is fine don't worry you'll be happy believe me .