fasttoys the s10 is 57/43, I would probably agree with your 65% front bias because the seating position of the coe isnt that much further forward than the s10, just a lot higher in the air.
I weighed my 3600 s10 at the scrapyard for a shipping estimate and it was 3160 lbs (after subtracting myself) so I would bet the sheetmetal of the standard 3100 is less than the s10 sheetmetal it replaced (I have speculated this several times in the past), so I bet your 100lb heavier estimate is probably pretty accurate too.
dsraven I bet even the wood bed weighed 3x the steel bed of the donor silverado he used.
I put some 1 1/4 thick cedar from a donor flatbed in mine and it dropped the truck almost 1/4 inch.
I have thought about a coe project for a while now so I will pay attention to how this all works out.