I guess if you're building a 400+ hp A series the 6 speed could be better, otherwise a 71C will live to more than what most A series will ever do. The 6 speed is huge, and the internal slave cylinder sucks, and shifter will need replacement too likely.

My TVR v8 has a world class Borg Warner T5 with 2.6 first ratio
and only weighs 35kg, are plentifull (use post 1985), sit behind v8s,
every gear ratio is available cheaper than other boxes, shifts like
a ferrari gated box and available in all any position stick location.
4 bolts undo the bellhousing and my TVR uses a 7.25 inch dual clutch
so less dramas and no need to resize your tunnel not to mention
the T5 is very compact, modular and easy to access the gears from
a top cover plate and removable front section.
71 series weigh 42kg and require alot more work to cut and shut as
they have a unitary body and bellhousing while the T5 is just a
removable bell that is accessible from the outside making gearbox
changes a breeze and even clutch changes just as easy.

If you use a simple adaptor plate on an A series Auto bellhousing
then the T5 mated to the bell requires no cut and shutting.
The plate would only need to be 5-6mm thick and hang onto four
countersunk bolts to the front of the T5 unit.
Clean and simple with no precision cutting and welding etc.

An A series T5 conversion kit would make this gearbox more attractive. Sounds like a good little project for someone with more spare time than me.

Just saw the conversion in the tech wiki