Make sure your full size bricks are 4 1/2 X 9 inches................. AND you have two draft caps on the front, not one making it a Baby Bear;
The brick dimensions E,F,G,H are for the first style box with angle iron corners and flat top doors. No tags, but model I and II. The drawings shown in post #2 above show the bricks in-line, not staggered. (flipping sides) It doesn't matter if they are staggered or inline. It just prevents the straight crack between bricks. That drawing was before the brick layout was in the first manual.
Page 9 in the VI manual from 1978 shows the same layout and is pictured with the same letter designations for brick sizes. (you may or may not have the second brick course)
![[Hearth.com] Mama Bear Firebricks [Hearth.com] Mama Bear Firebricks](https://www.hearth.com/talk/data/attachments/144/144252-6ea2ffe2015d5e4e529b9073d6715f0c.jpg?hash=giJRxd3BHq)
The Mama Bear drawing in the 1980 VI manual (bent corners, arched top door) shows them staggered on page 12. That is a later stove, but the bricks are the same size. (It also shows a second course you may or may not have) The letter designations used are B,C,D,E but are the same size cuts.
Yes, the back goes in first, 3 full bricks should fit across the back and need one more 1 7/8 to complete the back. Then fill in down the sides with full bricks (5) that should leave you needing 2 7/8 to complete the sides to the front wall. It can be a snug fit and can't have any ash between them at all. Lay in the bottom starting at the back, and this pushes the side bricks tight to the sides holding them in place. That should leave you with the same space at the front as you had on the sides. About 3 inches for the 2 7/8" pieces.
If the back fit with 3 full bricks and one cut 1 7/8 wide, your stove width is normal, and the bottom should fit across the stove correctly.
If you don't have enough room in the front for the 2 7/8 piece, your stove length must not be the normal size. How much room are you left with to fill in when the bricks are pushed tight??
The sides and bottom will come out the same since they are both pushed back against the back bricks.