Many Diesel compression testers have common adapters included or available to fit most anything, including Kubotas. They'll usually say so right on the box/product description.
Just shop around.
Even Harbor Freight's tester lists Kubotas, if you want an econo model.
Yes either injector or glow plug. Depends on the tester, some have fittings for one or the other, or both.
I'd say glow plug is most common, and usually easiest because you don't have screw with injector lines/possible contamination, and replacing heat shields/gaskets, which you're supposed to do whenever you remove an injector.
I agree the glow plug holes are easier access - also good time to test them (connect 12v jumper cables & see if the end gets red). What symptom does your L2550 have that is prompting a compression test?
When you do connect the compression gage, remember to disable fuel flow at the rack. You do not want the cylinder to get any fuel while spinning the engine over during test. It will blow up your test system... KennyV
I agree the glow plug holes are easier access - also good time to test them (connect 12v jumper cables & see if the end gets red). What symptom does your L2550 have that is prompting a compression test?