I love the build and adding the subframe connectors will help.
But I disagree about the upper crossmember. When the original transmission mount is in place the upper hoop of the crossmember triangulates that whole section. And the fact that it's welded to the floor pan further stiffens both the floor pan and the crossmember. Now, the new transmission mount/crossmember is definitely more stout than the original, but even with that being the case I'm not sure it truly makes up for the loss of the upper hoop of the original crossmember and how it's tied into the floor pan.
I don't think you'll have any obvious problems, especially with the subframe connectors installed, but in a torsion bar car where the suspension loads are carried by that crossmember I'm not a fan of losing the crossmembers upper hoop. Just my opinion.