With the trans filter back on and the pan back on and 4 quarts of new trans fluid back in the pan.
Put a "T" with a 10" long rubber down hose on it and plumb that in on the passenger side trans cooler line before it enters the radiator.
Put the 10" long rubber down tube into a 1 gallon old plastic milk jug, with the jug sitting in an oil drain pan.
Now start up the engine and when the milk jug is half full of trans fluid, shut the engine off. Then put 2 new quarts of trans fluid in to replace what just came out. Repeat until the trans fluid coming out of the "T" is clean.
Tip: You can plug the T line down hose, after running a fresh gallon of trans fluid through the trans then fill the trans to the proper fluid level. If the trans fluid still looks dirty, keep flushing it out 2 quarts at a time till running clean.
Start > pump out 2 quarts, shut off > put in 2 new quarts trans fluid to replace what just came out. Repeat as needed until you are satisfied the converter has been flushed clean.
Remove the "T" and down hose, reconnect the trans cooler line to the radiator.
Top off the trans to the proper fluid level, idling in neutral for the 727.
And yes remove the balance weights on the 727 torque converter if they are on there, make it neutral balance. The the Magnum flex plate already has the proper weight added for the external balanced Magnum engine.
☆☆☆☆☆