I would assume the door panels and seat patterns would differ..I don't have an AMT '68 Chevelle annual to compare. The Modelhaus does have the '68 dash available, separately and as part of their '68 conversion kit, which includes front and rear bumpers, taillights, and dash.
For a chassis, I think some have used the more detailed AMT/MPC '69 Cutlass chassis under the AMT '69 Chevelles before...