Depends, if you have a parts car or know of a car at a local wrecking yard with intact manual tranny parts, I'd say the rating to be about 3 or 4. There is no drilling to be done, just need clutch, brake pedals, master cylinder hydralic line, actuator. clutch and flywheel.
2.5 if you have the parts like he said, 3 or 4 if you're dropping in a complete 5-speed driveline (with differential) out of a 280ZX N/A, maybe 6 if you go with a turbo diff with CV joints. A BMW 750iL V12 swap is a 10+, using an R-200 ;-) !
I'm about to do one myself. Be sure to get the pedal bracket assembly (looks like a bitch to install), engine backing plate (different on standard), boots for the shifter/console and hard line between the clutch slave cylinder and clutch master cylinder. You will also need to install a pilot bushing in the end of the crankshaft. Driveshaft should bolt right up and you may have to tinker with the speedometer cable gear.
I'm getting ready to by my first Z -- finally! I've found two, a '75 280Z with auto and a 77 280Z parts car with a 4-spd. I want to pull the 4-spd from the parts car and put it in the 75. I found this message in the archives and wanted to find out if you did this and how it went.