Hello and thanks for using Just Answer.
When you had the chains off did you mark the chain itself by lying it flat and marking the single link at on end and the two links at the other end?
OK so the right side had 3 mark in this picture?
Alright so it does sound like you have all the marks lined up correctly.
When you crank the engine does it seem to be a normal crank. Steady and does not seem faster than it used to?
When you installed the trigger wheel for the cranks sensor it should of been marked with either front or rear, was this installed correctly?
The plane of the head would be parallel to the flat surface of the head. As far a clock positions go, they are only good for getting close to where the marks need to be. The only true way to accurately time the engine is with the marks on the chains and gears. If you followed the procedure as you said then the cams and crank should be in time and going back and forth with you it sounds to me that you have it timed correctly. If it was off by one or two teeth it would still start, but it would run pretty bad.
I am thinking your problem is with something else like a possible crank signal concern or something else that may have been disconnected that may have been missed during assembly.
Is it possible that one of the cam gears moved by 1 revolution and now even if the timing marks are correct, the engine wouldn't be timed correctly? or is this not possible. Or is there another way to see if the cams are correctly, like the crank at TDC and the cams or something else at a different angle, because what if one of the cams rotated more than the other, because the chain snapped when it came off the gears and the cams moved, i just don't know by how much? is this possiible?
The cam gears can only go on one way. They have dowl pins that go into the camshaft and can only go on one way. Usually when the move when removing the chains, they only move a matter of 3 or 4 teeth.
The only way to check if the cams are timed correctly with the front cover still on is as you are doing it with the clock positions and this can only give you an idea that you are close. If you have the crank pulley at TDC and the cam marks are pretty close to the picture below, then even if you are off one or two teeth it should start.