It’s true – I can’t leave well enough alone.  I’m starting to tinker with the idea of installing the 3.9l Rover V8 I have in my garage in this car.  There is no way the stock drive train will take that much power without modifications so I’ve decided to ditch the triumph parts and go with something more modern and maintainable.  The first step in redoing the rear end is to replace the stock differential with a newer unit.  I came across a website in New Zealand with a guy who had installed a Subaru / Datsun 510 rear diff into his car without modifying the frame.  After talking to him at length I decided to copy his route.  I wanted to install the differential without making any changes to the frame whatsoever.  This meant that Mike and I had to modify the differential to get it too fit.  We fabricated an adapter plate that converted the front four differential mounting bolts into the two triumph mounting bolts:

We also machined a replacement rear differential cover plate which allowed the differential to bolt right up into the spitfire frame the same way the triumph differential did.  Finally, we welded onto the differential a mounting plate for the leaf spring.  Although I want to end up with coil over shocks, to initially test this unit – I want to keep the stock swing-spring setup.

Three axle adapter plates were machined.  Two for the output shafts and one for the input shaft.   These plates converted the Datsun / Subaru bolt pattern to the triumph bolt pattern.  The output shaft adapter plates also made the width of the differential the same as the triumph unit so the stock half axles would bolt right on.  Installation of the unit took a few hours.