Typically the cranks are either 3/4” or 1”. Measure the clutch and you’ll know which to get.
If it’s a 1” clutch you can also get spacers/adapters to space a 3/4” clutch to fit.
That said getting a new clutch is a good way to go in case the crank on the existing engine has some unusual length or taper. Looks like there’s already a spacer on there.