Q: Engine swap ls400 Lexus 1990 to 1993 1UZ-fe

The engines themselves, that is the blocks and cylinder heads, are identical in both model years. So, they are a direct catalog interchange, have identical castings and so forth. However, the computers for the two years do NOT interchange. That raises the distinct possibility that engine management controls, including any and all electronic components and sensors, from the 1993 model year engine will be a mismatch for your existing 1990 engine computer. You will either have to check the part number of each and every such carried over component (actually not hard to do using on-line Toyota catalogs) to confirm exact catalog interchange or simply just carry over all components from the 1990 engine to the 1993 engine. It is also possible that components other than the long block are not identical such as manifolds, the throttle body and so forth. Basically, the engines are interchangeable but you will simply have to pay close attention to the components and controls attached to the engine so as to avoid computer issues. If you need assistance with your engine replacement, YourMechanic professionals in certain locales can assist with that. Please simply inquire based on your locale. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.