Speedometer cable length, from the Service Parts List:
For RHD, 5' 3", or 63 inches.
For LHD, 5' 6", or 66 inches.

The speedometer cable starts at lower right of gearbox tail housing, runs forward along side of the gearbox, goes up the right side of the bell housing. For a Left Hand Drive car, it attaches with a P-clip and hex nut to one of the bolts at lower bulkhead plate to tunnel joint one position shy of the center. Then it goes over the heater shelf, past the heater, and through the bulkhead to the speedometer. If the speedometer is in the far left position of a LHD car (not standard configuration), the cable runs under the master cylinder.

The longer LHD speedo cable is often supplied for RHD application (to reduce inventory).

Tachometer cable is same for all MGA.
BMC# AHH 5354 -- SMITHS# DF 118/00 -- Cable Length: 3' 2"