Only real way. Never seen an elaborate fitting for the injector hole, plus you'd make a mess with the oil and diesel.
Get an M10x1.0 O-Ring boss male to 1/8"NPT female adaptor. Thread in a 12" grease gun whip. On the other end, a 1/8" NPT barrel connector (female both ends)
If you don't have a diesel compression tester, get Harbor Freight's cheap one. It'll have a small 1/8"NPT adapter you can thread into your newly made adapter.
And yes, it needs to be a whip. A solid one will hit the rocker arm.
Glow plug hole is where you screw you CT fitting into. I just did a compression test on my 1500 truck today. I had 1 low hole(150lbs) Remove all your GP's before you do this test. As stated above: you must have a whip fitting.
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