The engine needs to be "configured" the same, or newer than the year of the chassis. That means, for the OP, he could install an '88 SBC, as long as all sensors, ECM, etc, were the same as a '94.
Of course, this totally excludes a carburetor on any sort. Also, a strict interpretation of the CARB rules require the transmission to match the engine; IE: Chevy's never came with an AW4 trans, or, Chevy TPI engines were never attached to NV4500 5 spds, so these combinations would never be smog legal. The safest bet to get by CARB, is to install the complete engine/trans and ECM/PCM out of the donor vehicle, and insure the donor is the same year or newer than your '93. My CARB inspector actually scanned my ECM to insure the correct EPROM was installed. And of special interest to XJ's are exhaust manifolds. Frame to manifold clearance is a major problem with the XJs. Trying to drop a '93 or later truck SBC into an XJ will require extensive mods to the frame rails, or will require use of manifolds not CARB approved. So when deciding on what engine configuration to assemble, make sure the stock manifolds will fit between the frame rails, or be ready for major "slash and burn".