Best manual transmission for an LS swap

• Tremec TKX (5-speed): 600 lb-ft; the slimmest option for tight tunnels; 3 shifter locations. It does not fit some swap kits built around the T56 (e.g., V8 Roadsters' Miata kit).
• Factory T56 (6-speed): plentiful from F-bodies, GTOs, CTS-Vs and Corvettes; factory ratings about 330–550 lb-ft across versions (F-body 350–450); big, so tunnel work is common.
• Tremec Magnum (6-speed): 700 lb-ft, 135 lb dry, 2.66 or 2.97 first gear, double overdrive; the aftermarket T56 upgrade.
• Magnum-F: a 700 lb-ft drop-in replacement for the 1998–2002 F-body T56 (also used in LS-swapped Supras, RX-7s and Datsun Zs).
• Magnum-XL: 700 lb-ft; the GM version includes the bellhousing, crossmember and shifter.
• TR6060: derived from the T56; used in the Camaro SS/ZL1, CTS-V and G8 GXP.
• Budget: a World Class T5 (300 lb-ft) is marginal for LS torque.

You'll also need an LS-specific bellhousing, clutch/flywheel and hydraulic release.