Electrical 1991 5.0 battery size

[7991LXnSHO]

The catalogs call for a group 58 battery in a 91 5.0, but the tray I have has room for a longer battery. It clamps side to side fine, but there is approximately two inches of space front to rear.
Was there originally a bigger battery specified (like an old 24F?) , or did somebody put in a different battery tray? The tray looks like a factory black fiber one with the single bolt plastic wedge.

 

[Wayne Waldrep]

I believe that is normal. The 58 size is correct.

 

[7991LXnSHO]

If this is normal, I am thinking about cutting two pvc strips from brick mold or other trim and gluing them into the battery box to reduce the chance of the battery sliding front to rear if the clamp gets a little loose. The box looks just like what I remember in my 79, just on the other side.
If a group 58 has plenty of CCA, putting in a bigger battery seems like a waste of weight. But I do not want a battery sliding and cracking the tray or hurting the overflow tank lid if I go auto crossing or driving enthusiasticly.

 

[Dan02gt]

I have a group 65 AGM in mine and it fits perfectly in the tray.