If all you want is lockup you can accomplish that with he 727 you have.

You need the converter, valve body and reaction shaft support (or pump asssembly).

I would use the later electronically controlled lockup valve body.

You would have to do the same on the 904 if it was. It a lockup unit.

Nice thing about the 904 you can find a low gear set that will make it scoot a little better off the line and not screw up mileage.