You can repeat the compression test when the engine is fully warmed up to see if that makes a difference.

A compression leak test is indeed done with a compressor, but you need a reduction valve, so that the air pressure is lowered to around 2 bar. Ideally you need a gauge, so that you can determine the amount of leakage (in %). Here is a diagram from Wikipedia so you can see how the gauge works:



Source: File:Leak down tester.GIF - Wikipedia, the free encyclopedia

Injection pump usually lasts several engines, so it is an unlikely candidate, but it is not impossible. Injection pumps are indeed tested in the way you describe, but on a test bank, see the picture below.



Blow by is normal, even non-shaking engines have that.

The problem with using nozzles which aren't designed for your engine is that you never know which problems they can cause. Diagnosing problems can be more difficult, because there aren't any specs with which to compare.