You've done something wrong converting kg/mm to lbs/in. Lbs/in should be 56x kg/mm, so 6kg should be 336lbs.
How have you come up with the front ARB rate? If that was from my post that was only approximate to give an example, and doesn't reflect the actual wheel rates as the ARBs operate on a different motion ratio to the springs.
I've realised what you've done with the spring rates now. The ones I quoted were in roll resistance per degree of roll, that's not a simple equation really. The standard EK9 does work out to roughly those numbers, but I had a large spreadsheet to calculate it all.
I've since then changed the spreadsheet as figuring out roll resistance in terms of lbs/in/degree was confusing, I now just add the wheel rate contributions from the spring and arb for both axles.
To get wheel rate you multiply the spring rate by the motion ratio squared, which in the case of an EK is around 0.7 front and rear. So your 250lbs would be 250*.7^2 = 123lbs.
The standard EK9 ARBs have wheel rates of roughly 170lbs/in up front and 280lbs/in in the rear.
So overall for the standard car, the front has 123+170=293lbs/in and the rear has 123+280=403lbs. Overall, that's 696lbs/in and a 42.09% front roll distribution.
Since you sound pretty interested in all this, fire me an email address over PM and I'll send you my spreadsheet.