Luke (RoguePro5) and I had the transmission in and out of my Miata in 5 hours. That includes a 20 minute parts run, and who knows how much standing around BSing. The transmission swap itself is quite straight forward.
You'd have to add a clutch master cylinder (mounting points are already existing), slave cylinder (mounted to the manual transmission), plumbing to both of the aforementioned, installation of the clutch pedal (bracketry already exists), and a swap from the driveplate/tourque converter to flywheel/clutch assembly (10 mins). In regard of the transmission, the swap would be very easy to someone who had a few hours and an extra set of hands.
I'd say a good 12 hours and the swap would be complete. If you were closer, I'd be willing to lend a hand. Feel free to drop me a line with any questions.
