As of late, I've seen problems that some guys are having because of distributor drive gears being installed 180 degs. off or not where they wanted #1 to be located. This is my suggestion to eliminate distributor alignment problems. first, install the distributor hold down clamp loosely. Next install the 2 shims and the drive gear. Now install the distributor, tighten the collar's 13mm nut and position the reference notch, the mark on the distributor's rim, where you want #1 to fire. Finally, line up the rotor with the notch and lock it down. I'm taking it for granted that an engine stand is being used to lay the crank or the left case half, #3 & 4, is laid out flat and level. With #1 and #2 rods in hand, lay the crank in the case. when seated correctly, #1 will be at TDC and so will your distributor. Now you can drop in the cam and line up your reference dots by simply rotating the crank slightly until the marks are visible allowing the cam to be dropped in and perfectly aligned. I've had good results with this procedure and hope my process description is easy to follow.
Ainokea