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I am certainly not an expert on autocross, but have some suggestions/comments.
Coilover suspension. Converting to coilover on a car without a frame can be a very involved process in terms of what has to be done to make strong enough mounts to take both the spring and shock loads. Not easy and certainly not something for the casual autocrosser.
Competition springs - IPD has not made competition springs for about 20 years.
The rates for the springs they have been selling, whether the saleman said they were competition springs or not, are approx. 320 lb. front and 150 rear. The problem with these rates is that they, the fronts especially, are not stiff enough for hard cornering, and certainly not competition, but are stiff enough to adversely affect ride quality. That's the reason for our progressive rate springs that have a high rate of 500 lb. The progressives might not be the first choice for a pure autocross car, as even stiffer springs would give better handling ( we use 1000lb. springs on the road race cars ), especially with stickier tires, but they are the best compromise we have been able to come up with between street where ride quality is still important and the best handling in corners.
Shocks - no mention of shocks here,and they are critical. One of my questions from watching the video and seeing the handling in transition would be what shocks are being used?
Sway bars - critical to tuning handling. Too many people just bolt on a set of
IPD bars front and rear because that is what they have been selling and seem to
feel that they are an instant cure for all handling problems. One size fits all simply does not work. Competition sway bars are adjustable. IPD used to sell adjustable bars. They have not had the adjustable fronts for over 15 years and the adjustable rears were phased out more than five years ago. Beyond adjusting in competition, an adjustable bar can be set up stiff for an autocross and then adjusted soft to go back to street driving. My feeling is that the IPD bar is too stiff for normal street driving, but not stiff enough for competition. We usually find that the best setting for the rear bar is the softest - off. Try it by simply disconnecting the link on one side - allows you to try in on and off with only a couple of minutes work, no need to remove the bar.
Limited slip differential - You really need one. They are readily available for the dana 27 and disc brake dana 30 rears. Very hard to find for the 67 - 69 drum brake dana 30s with the coarse 10 spline axles. The stock type LSDs can be shimmed to make them stiffer, and this can be used to help setup the handling.
No time for more now but hope this helps.
John
VPD, V-Performance.com
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