Linked below is a guy's video explaining Ackermann in the clearest and simplest way I have found, definitely watch it if you want to be able to steer your kart without the front wheels scrubbing and sliding. When you reach the 5:00 minute mark, he explains how you can use those 90-degree spindles just as they are, by bolting the pitman arm ends of the tierods separately instead of on the same bolt. The ends reach an inch or two further, going past themselves to reach their bolt holes. Gives same exact Ackermann for either leading arm or trailing arm setups, without having to change the angle of the spindle arms.
GoKart steering explained,including Ackermann Theory.WATCH BEFORE YOU WELD! - YouTube
That was a good video.... most valuable part to me was to get your angle on the spindle arms to meet at the center point of your rear axle which makes sense to me to get the proper arc on the inner and outer circle of your tires. I think I can accomplish this easy enough by adding brackets to my rear facing spindle arms to connect the hiem joint in the proper spot.
I'm using a steering rack, so..... I think the concept is still the same as a single pin pitman arm. I had originally built a steering box that was 2" wider than the plans called for, in large part because I knew I was going with the 11" rack and I wanted the pivot points of the rack hiems to be similar to the A-arms, and it turned out fairly close. I'm actually intending on cutting off my steering box nose, and redoing it because it ended up a little twisted and off level from the rest of the frame. So I'll have a chance to make the width "exact" to whatever would be appropriate, or, attempt to.
What I can't really wrap my head around - is while in a turn, and hitting bumps, the pivot point of the rack hiem will still be off from the A-arm joint, so, I don't know how you can avoid bump steer in a corner. I think the best I can do is avoid bump steer while driving straight??? Thoughts gents?