Steve,
Corner-Weighting your Cobra is a VERY precise measurement. It is also VERY in depth. It should take about 4-5 hours for 2 people to tune the suspension properly. It is more than a matter of simply turning spring height to suit a certain "feel". But a balanced car is worlds above an unbalanced car. Ready to dive into information overload? Here we go...
I see your posts of your measurements. You want to have your cross/diagonal weights equal. For example (LF + RR) = (RF + LR). In your case (720 + 717) = (708 + 684). (In other words 1437 vs. 1392) You are 45lbs off diagonally. You are affecting how the weight transfer is applied, side to side. This will give you a balance upon L&R cornering. In other words, it will handle left turns the same way it handles right turns. Do not worry about Front to Rear balance for now.
To properly weight the car...
1) Your scales must be level to within 0.060 inches of each other. NO garage is level. Use laser leveling system to shim scale height.
2) You must have the anti-roll bars disconnected.
3) You must have EXACTLY the same air pressure in each tire
4) Must have 1/2 tank of fuel
5) Must have driver sitting in the seat, helmet in lap, with all the crap out of the trunk, (ie. be in race trim).
In conjunction with corner-weighting, you must have alignment tools to measure the camber, caster, and toe. Changing the ride height on a corner can change your camber gain by as much as 1-2 degrees. This would greatly affect handling.
So what you do is get "close" on the corner weights, then take suspension alignment measurements (camber, caster, toe). Write those down. Adjust the alignment to whatever your manufacturer recommends to be suitable for your intended application. Then check out the corner diagonal weights again. If you are within 10 lbs on the diagonals, that's close enough, leave the corner weights alone & mark the spring collars so you know not to move them from this position. As long as your alignment is where you want it AND your corner-weights are within 10lbs diagonally, you're perfect.
Now back to the Front to Rear balance thing...
When done, you may raise or lower the rear or front to suit your "front to rear" balance needs. BUT, you can only move them in pairs. In other words, move BOTH rears up, or BOTH rears down. Or both fronts up? Moving them in pairs will not change corner-weights because corner-weights are measured diagonally. Just remember that you might be messing up your alignment if you move the front pair. I would suggest (raising/lowering) the rear pair a bit to suit your needs. And set rear tire air pressure 2lbs less than the fronts.
And dont forget to put the anti-roll bars back on.
With track experience, you will discover new alignment settings to fine tune your car for even more handling! But that comes in time...
I provide this explanation only from personal experience preparing my racecar.
Happy motoring!
Stephen
Cobra University
stephen@cobrauniversity.com