Would you notch a 727 bell that already has an inspection port in it?

The flex plate needs to be from the 5.9 to match your 5.9 engine, as it is externally balanced. The torque converter needs to be neutrally balanced, so as not to affect the 5.9 engine's factory flexplate balance. If you add that weight from the torque converter, you will have thrown off the balance provided by the 5.9 flexplate and harmonic balancer.

I had to file on the side one of the 4 mounting holes on my 5.9 flex plate to bolt it up a neutrally balanced torque converter for my old 727.

Once I built a neutrally balanced Magnum based 408" stoker, I used the neutrally balanced 5.2 Magnum flex plate and had my custom converter made with the pads in the correct place so I didn't have to file one of the mounting holes for it to fit.