The engine doesn't necessarily need to come out, but.......
the trans has to be separated from the engine to get access to the flexplate/flexplate bolts by a long 3/8" breaker bar, I say 3/8" because it is less bulky than a larger 1/2".
The paraphernalia from above the trans has to come out, *battery, exhaust crossover*....etc.....the driver's side axle shaft needs to be pulled out from the transaxle, the right side released form the trans, the transaxle support bracket will need to be removed, the engine will need to be supported by an above hoist/engine bay support, one could put a support under the pan but I don't recommend it. Drop the starter, Pull the bolts that hold the trans to the back of the engine & slide the trans back enough to get room to get at the converter flexplate bolts and then the crank to flexplate bolts.
One could attempt to move the engine forward but the LQ1 engine mounts are a pain-in-the-ass to get to without lifting the engine up, it's a sort of *six -of-one-or-half-dozen-of-the-other* situation.
It's not a fun job at all, and not especially for what you're getting involved with.