I would gusset the sides of the brackets on the block, and put a gusset to tie the two tubes of each frame mount together. Probably one at the frame and one at the crossmember too.
I take it you intend to use a similar bushing setup for the trans mount to take the fore and aft load off these, and to be consistent hardness of rubber?
They are nice looking, not trying to bash or anything, I do tend to overbuild.
