WRT diff cover gaskets, I like LubeLocker's for no-mess install (or removal). I've using them exclusively for 25 years with zero leaks. Some aftermarket covers that utilize welded steel gussets tend to be "less than flat", thus need a complete bead of RTV sealant. No problem with LubeLockers on OEM stamped covers or (in my experience) aftermarket cast or nodular iron covers.
Dana 30 / Dana 35 was standard (Dana 44 rear optional) on all but the 2003-2006 Rubicon which utilized Dana 44 front and rear. Your front if original is a Dana 30 and your rear as already confirmed is a Dana 35. LubeLocker gaskets are available from Amazon and elsewhere.
LubeLocker Dana 30 LubeLocker Dana 35