you can still get the gas tank ones from the dealer, they call them frame reinforcements, passenger side = 52001174, drivers side = 52001175, they're around $20 ea but if it's a later model XJ it would already have the passenger side one used for the exhaust hanger.
Not sure about the t-case, I re-used my stock front bumper hardware to makeshift nutserts for my stock TC skid.
-Bic