[38bill]

'38 - '41 should be the same. Here is my '38.

The top board is 3" wide for both the front and the rear.
The bottom front block is 3-5/8" wide.
The bottom rear block is 3 1/4" wide.

Front blocks are 7" long.
Rear blocks are 5" long.

Top boards measure 45-3/4" (front) and 45-1/2" (rear). The front board is tight and the rear is loose so it looks to me that they could both be made the same at 45-5/8".