You should be aware that this is not a simple modification
The pedal crossmember will need modifying substantially as will the centre panel of the bulkhead.
The gearbox crossmember is in the wrong place, and the floors will also need modifying (they are steel on 1970 models)
The transmission cover is a very different shape and won't fit over the t5 gearbox, and the gear-lever is in the wrong place. The handbrake lever will no longer fit and will also need to be changed
That's just off the top of my head...
I would urge you to try one of Billy Bellingers full synchro Moss box conversions, they are almost rifle bolt precise, and very nice to drive with
Simon @ Sifab.co.uk