the engine w/o resistance. You must be careful as you undertake this task since the pistons can make contact with the valves and bend them. Determine how far you need to move the crank to get the mark back near the "V" grove on the oil pump lip. At worst you are 180 degrees or 1/2 of a rotation. The cams run at 1/2 crank speed so you will have to move them half as much, at most 1/4 of a rotation. carefully move the motor in 10 degree increments watching for resistance due to valve contact. You coud use a helper to move the cams while you rotate the crank. Not sure there is another way but someone else might chime in.
Alternatively, you can count teeth and draw new marks on the belt and install it that way. Move the reciprocaing assenbly to where you want it and verify your positions.