using dougs photo (thanks doug!)....

the little red arrows are pointing to the bolt holes on the "open" face. They appear pretty filled in...maybe layers of paint from sitting in a mueseam? Or maybe even the factory filled them with some sealer of some kind... i will admit that the holes dont show up real well in period photos.
Easiest way to add these is to make a little jig out of scrap plastic with a plate of plastic with the location of the four holes marked, and drilled through the plate, and a peice of sqaure stock glued to the back that acts as a vertical alignment guide. You just rest the square stock on the top of the bogie, center the jig left/right with your eye, and then take a sharp object (or small diameter drill) and mark through the jig the location of each hole. Remove the jig and drill the holes in the bogie at the marked location.
Of course my version of the jig works before you glue the skids down...
in your case just choose some other point to align the jig plate with (maybe across the front, from the side, or even below)
Save your jig for future projects!
as for those bolts holding the return roller bracket...i personaly never add them because you can barely see them...but I havent reached the advanced stages of shermanholicism yet!
Andy