There is NO difference between B2 and B3 chassis plate. Concerning the worlds style shock tower on the rear: I think it was an upgrade, yes.
Another difference between B2 and B3: CVD's look different on the B2, like on the T2 truck. B3 (not the sports kit) came with MIP style CVD's
B2/B3 skinny wheels on the left - wide wheels (the same as B4 wheels) on the right (Upgrade)
rear B2 chassis plate on the left - rear B3 chassis plate on the right
B2 on the left - B3 on the right. Note the difference on shock tower, shocks, top plate, arms.. (last B2 models had the same top plate as the B3, with holes for a anti-roll bar on the front)
Rear B2/B3 shock tower on the left - worlds (B3) option part on the right
