I'd not seen a horizontal worm & 90° gearbox in a starter set Lionel before. Just horizontal motors, parallel to the axles.
Is the weak link the traction, the motor, or the gearbox failing? Can it handle more if weighted for traction like some other small can motors, or is a hot motor or weak stall torque or prone to stripping the box? Slipping of the drive gear press on the box?
I think I want the motor & gear assembly for a bash if the gearing is of decent strength; I need the 90° offset and don't want to foot the bill for brass; the rpm range isn't even an issue.