I understand that one can bolt some sort of flat board onto the engine inplace of a prop.... but whos to say that the engine is correctly mounted to the engine mounts (could be 1-2deg right, left, up or down).
You are.
The whole deal with using accurate measuring tools is to find out for ourselves.
We have a slight advantage when checking out a model when we have the instruction booklet and it's got the setup information in it and the booklet is correct. Often we don't have a booklet. Even when we do, it often has nothing about this stuff. And even when it does, it's not always the truth. I've got an "excellently complete" booklet with my Phoenix Sukhoi that says the airplane has no down thrust, no up thrust, no right thrust and no left thrust. And later on in the booklet they show a diagram for mounting the motor mount that would be perfect for a firewall that had right and up thrust. And it turns out that the bloody firewall was built into the front of the fuselage with right and down thrust.
The truth is, if you're wanting to verify that the factory built the model "correctly" you're SOL. Out of Luck.... None of them want you to know how far off or how accurate their workers do things. So don't expect to easily find all the numbers.