Equivalent to FIT0450 TT Motor with Encoder (6V 160RPM 120:1)

Hi I have a project and it need to drive 2 motors with encoders. The encoders will be used to calulate distance,

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The motor motor driver runs ok with 2 x FIT0450 TT Motor with Encoder (6V 160RPM 120:1), but if I connect 2 x  FIT0520 

Metal DC Geared Motor w/Encoder - 6V 300RPM 3.6Kg. only one works. 

Both motors run OK when powered directly with 6V
I cant use the FIT0450 because of the spindle orientaiion, so is there an equivalant  to this motor where the spindle is at the end the motor, not at right angles?

I would prefer a metal geared motor but a TT model will do for now?