1970 Dart 340 Swinger trans swap American Powertrain or Silver Sport Transmission?

Looking for insight on what others have done. Has any used the 5 or 6 spd trans kits from American Powertrain or Silver Sport? My car currently has the factory 4spd in it and I want to upgrade to a 5 or 6 speed and trying to figure out which kit is the best between these two.