Mark the crank and camshafts, rotate the crank through 360 degrees and all the marks shoud be back where they started. If they are not then you have probably bent the valves trying!
ERRRRR! I hate to disagree with a RegRep but that aint so.
If you rotate the crank 360 deg then the cams will only turn 180 deg leaving the marks nowhere near the belt itself!
Rotating the crank another 360 deg will bring all the marks alongside a piece of belt, BUT NOT WHERE THE BELT MARKS ARE unless the belt is exactly twice the length of the distance round crank pulley, which it ain't!! D'ya see what I mean?
Lets say there are 36 teeth on the crank pulley and 72 on each cam (the actual numbers are irrelevent as it is all a question of percentages) then one turn of the crank moves the belt 36 teeth and two turns moves it 72 teeth. Not far enough to bring the white marks into play
On this scale the belt is gonna be 216 teeth or another multiple of 72 or else the marks would only line up very rarely.
If there were timing marks like on the old "Nord" or "Sud" engines, ie on the engine block/head and on the pullies, then yes you would be right but when the marks are "on the belt" as described by iceman then things are different.
Cheer up Iceman you are OK!