it's not exactly true.
It is a bit short but the width is within hairs of the AMT and newer Revell '69 kits.
I used some parts on my '70 build and had a front bumper from the MPC kit ready to go for it if I couldn't find a useable original or resin part [Thanks again, BTW] Just took a couple file swipes on the outer ends of the bumper. Back bumper is also the same width, BTW. Bodies are the same width, no problem there.
The wheelbase will also work a the axel holes line up quite well with the original AMT wheelbase in spite of the MPC kit being shorter. Don't know how that works for the MPC kit actually as the wheelbase is too long for the MPC body. I even used the MPC kit's rad and fire walls.
The interior will work. door panels look the same as the original and even the seats are only different in the number of pleats.
In fact, I only need another replacement '69 body for the extra length [and rear wheel openings which are now on my '70] to make a pretty presentable '69.