What is this bracket called

It may not look like much but like stated already, that stamped vertical support/bulkhead is there to tie everything together. There's one in the rear too where the front spring perch is. If you can't find them from AMD get someone to cut them out of a parts car and make sure they get some of the surrounding pieces so it can be lined up properly.

Think about it - by removing that bulkhead you'd be left with an open space between the inner and outer structures with a lot of force acting on it when the engine torques over. Is it better to have a solid support all the way around that area or just a tube across the bottom? IMO, you would make the structure weaker by eliminating that bulkhead. Plus all the heat from fully welding around the ends of the tubing - forget it.

If you went full tube frame then sure, go for it but for now you're still mostly relying on the unibody structure for strength so don't compromise it. The cage will help some but it's not tied into that point. The hemi will be a lot of weight in front too so consider that as well.

I even looked through the Motown Missle book to see if that piece was eliminated on any of those cars and as far as I could tell, it wasn't. If you have the book, look on pg. 86 there's a picture of Don Carlton's Demon - that bulkhead is still there.

I'm no expert though so maybe @HemiDenny will chime in since he rebuilt Butch's A/MP car.