From my FJ60 V8 swap build thread (cut and paste) -->
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Transmission: I already have an old-school Chevy truck bellhousing (cast iron, part #3925505) bolted to a Ranger Overdrive unit (that is connected to my stock H42 trans and splitcase). The LSx/Vortec motors bolt right to a SBC-pattern bellhousing, but there's one bolt hole that's missing on the Vortec block (no big deal, according to people making lots of HP in Camaros and such with Muncie transmissions).
Flywheel: Most of the 4.8 / 5.3 / 6.0 LSx cranks sit .400" closer to the rear of the block (as compared to a 305 / 350 SBC), so you need a thicker flywheel to compensate. Sachs makes an OE replacement for some of the 6.0 trucks with a manual transmission...part # NFW1050. Can be used a standard 11" Chevy 'old school' clutch when using a Muncie / SM465 type trans behind a LSx motor.
Pilot Bearing: To address the same issue as the flywheel...there is an LS2 pilot bearing that sits in the large opening in the crank (not as deep as a regular pilot bushing), and it will allow the transmission 'snout' to engage the bushing. Chevy part #12557583
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I don't know specifically if the conversion bellhousings allow the same clutch/flywheel as I run (the Ranger Torque Splitter acts as the adapter between my Chevy bellhousing and the H42)...but I imagine it would work. Unless the Ranger input shaft is not the same as an H42 (???).
I'm sure someone here can clarify, but at least there's some info to get you started...
- Brian