your suggested extra bracing looks good, maybe a little overkill but then again, you,ll have lots of horses in that engine bay
Only other suggestion I would make is to add a corner brace on the passenger side in the engine bay...just like the one above the pedal box area...TR1 & TR2 to TR8.
Have you thought about installing a propshaft safety hoop? just in case the prop "lets go"
...it,ll stop it making a mess of your legs
cheers
andy