I do plan on racing mine and beating the **** out of it so I probably will fab something to go back on the upper crossmember. I remember reading a tech article in Mopar Action years ago where they swapped a fatty modern OD auto into a B-body, they ended up slicing up the upper crossmember hoop to lengthen it and get the new shape right then welded the whole thing back in.
On another note
@jcolman are those subframe connectors being welded in or bolted? Bolting them is far less effective at stiffening the structure...