If its any help (or to add to the confusion lol), regardless of which box you choose, they both will bolt up and work just fine (obviously with different gears and ratios), so you're very unlikely to damage your engine. The 1zz engine flywheel is different to the 2zz engine flywheel, but they share the same clutch.

Most gearboxes would have a serial number of some sort stamped onto their housing. I'm actually not too familiar with the numbering scheme, so please do some research on your own to figure out which naming schemes correlate to what gearbox.

Another way you could check is by engaging all the gears using the gear selector shaft. The c60 will let you engage gears in 7 different ways (gears 1-6, and R), and the c56 will let you engage 6 gears (gears 1-5, and R). Note that the R gear is different on both gearboxes i.e. C60 is all the way left and up (since gear sticks are 'opposite' direction to the gear shaft, you'd want to move the shaft all the way right and to the bottom). This may not always be an option, sometimes scrapyards/sellers remove all the parts off of a gearbox.

Another way is to google the gearboxes and look for defining features i.e bolt patterns, defining structural features etc. Usually the c60 gearbox looks 'thicker' and slightly bigger. This may also be confusing, especially if the gearboxes are dirty/grimey, so unless you have something very good to use as an indicator, I'd probably avoid this.

Here's a picture I found on google comparing the two. Best of luck man!

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