I used the Hall box. You just need to dimple it where the rack mounts are.
Theoretically a box is better simply because it will keep out road debris and water better.
It is true that the later cars with the dropped battery do not use a box but part of that consideration is the access to the bolts against the battery box holding the rack support.
You can fix that by substituting Allen Socket head bolts for those two bolts but you don't often need to get to them. Probably once in a lifetime to service the rack.
Some of Hall's "upgrades like this require a little additional thinking or fabrication. You need to realize that Gary was a bit of a street rodder at heart and had little or no issues with a little creative thinking. The fitting of the battery box in my experience was the most extreme but not really an issue at all. Many have difficulty in thinking outside of the lines then, now and always.