Can I put a 99 GS400 engine into 97 LS400?
 

Last night I discovered my "rod knock" was very bad main bearings. No rebuild here as the journals are in bad shape on mains 2 & 3.

Looking for salvage motors in my area I found a 1999 GS400 with 94K miles, everything still in the car. I'm wondering if I can take the engine/tranny/harness/ECU out of that car and drop it into my 97 LS400.

Any insights are welcome.
Thanks

Maybe but that engine is VVT-I while yours is not.

is it possible? Yes.

Will not be cheap and will require substantial wiring. Also, will need to be done in a very specific way with ALL the parts from the '98 in order to be CARB legal (aka SMOG legal) in california. Just off the tip of my head you're looking at: motor, harness, all accessories, trans, flex plate, converter, custom driveshaft, swapping the rear end gears (yours will be too low), dash cluster harness, immobilizer keys, harness, sensor, and immobilizer ecu, EVAP equipment, air intake tubing and maf, and the main ECU.

Versus buying a $5-600 '95-97 long block from a yard (with warranty) and swapping it out.

agreed on both counts, it will be much easier to get a used long block of the same year so installation will be a breeze. even if you get that motor for free, you'll spend a good amount getting it to work VVTi and all in the 97. gl!