Thanks for the pic - I think the pistons should actually be okay with no movement. I think you'd still want a tiny bit though, or I'd be worried that when everything warms up the rods might expand and crash the pistons into the valve body deck, but let's put that aside because it's probably not the source of your problems.
In terms of torque converters all I do know is that you can't use a converter from an an AW7xL gearbox (i.e. lockup) in a non-lockup, as the valve bodies are different.
Thinking what else gets disturbed by an accumulator mod... do you remember re-seating the two pipes that sit in front of the valve body, on the pan side?
If you can't measure your line pressures, if it were me, I think my next move would be to take the valve body out and check/inspect I did everything right, and maybe try and get the matching number torque converter while I had the transmission back out.