27, 28, 29 Frames almost the same. Each years same frame for 2 door - 4 door -coupes- and special bodies.
Body bolt holes to frame same.
There is a difference in "D" Chanel on the lower side frame supports that reinforce center of longer frame side rails.
Also running board brackets and front spring to frame attachments.
'28 and '29 frames would have brackets for the support of Front brake hangers, which would be helpful. As the '27 had no front brakes.
29 has two shoe Bendix brakes as opposed to the '28 with three shoe Bendix brakes.
///////////////////
The '27, '28 and '29's, had different step heights, thus running board brackets were different each year. That is one reason fenders for each year don't fit as shape and depth of running boards are quite different.
'29 running board brackets could be moved upward.
/////////
More '29 Essex cars made, aprox 229,000.