A 1970 4/4 should have 2000E three rail box. Assuming right hand drive reverse was towards the driver then back. Later cars had the inferior single rail box reverse towards the passenger then forward if memory serves me correctly.
Burtonpower highly recommended for bits and great info in their catalogue. May also be on their website too ?
The only 'defect' with the single rail version is the input bearing rating as it is slightly smaller than the bearing on the three rail version. But unless your engine is mega tuned, and you use all the power, all the time, you'll never care.
The ratios are ideal, and the boxes that came after are no-where near as good for a sports car.