The R154 is basically stronger, that's the basic difference, lol. Stronger and bigger and heavier. The W58 can take about 350rwhp on a 7M before blowing IIRC, the R154... more... but both will break if you abuse them.
It's cheaper to use the W58, because you can get the correct bellhousing no problem. The R154 requires the 1JZ bellhousing.
To mount a 2JZ into the car you basically need:
- 1JZ engine brackets (stock 1JZ ones if you have a 1/89-92 car, Becauseican ones if you have an older car, unless you want to change the crossmember)
- Bellhousing (2JZ-GE bellhousing if using the W58, 1JZ-GTE bellhousing if using the R154)
- Flywheel (2JZ-GE flywheel if using W58, 1JZ-GTE flywheel if using the R154)
- Clutch (Any stock or aftermarket clutch for whichever tranny you use -- can use MA70 Turbo clutches if using an R154)
Then of course there's the engine management and wiring, which will need to be done by you or someone else who knows what they're doing.