If you want a true measure you will have to level the cruiser front to back and side to side, then, with the tires off; you would clean the top trunnion pin and remove the bolts holding it in, then measure across the top of the trunnion pin with tires facing dead straight.
Thanks for you input! There seems to be no starting level point to start, so I am just going to use a known point and see the difference available as I rotate the axle. Then I will head to an alignment shop to get a good measurement, make adjustments and try again. Trying a modified "washer mod".
I measured off the top of the knuckle, cap bolts before tear down. Then tore it down and measured many times off the bearing socket in the knuckle ball. This was after getting the truck at ride height on the shop floor and level. It is tricky to take a measurement since you want to be parallel with the frame rails. A long level with a digital angel finder built in works best for this. So I took reading after reading after reading. Cut the knuckle balls, rotated them to what I felt was 4.5*. Measured a bunch more and burned it in. Took it to the alignment shop and I got 4* one side and 3.7* the other. Camber is also near perfect so I didn't screw that up either.
Very happy, Cruiser driver like a dream now. Two fingers on the wheel at 80mph no probs.
BEEN DOING ALIGNMENTS NOW FOR 12 YEARS, ALL STATEMENTS ARE TRUE . MEASURING FRAME ANGLE IS VERY IMPORTANT WHEN SETTING CASTER, ALSO VEHICLE WILL DRIFT\PULL TO THE SIDE WITH LESS CASTER USUALLY - .05 DEGREE SPLIT TO LEFT WILL COMP FOR ROAD CROWN GOOD LUCK
I'm at 4.2/4.4 after building the axle. I measured right on the trunion races, anything else was vague. Even the flat high steer arms pose issue as you gotta be perfectly parallel with the chassis or the acuracy quickly diminishes with a slightly turned knuckle. The numbers ramp up falsely do to kingpin inclination when looking from front/back of the housing.