I regret to say I was around at the time for both P76 and P8! I was 18 in '71 and in my last year in 6th form. At that time the Times had a scheme to provide cheap (free?) copies of the paper to students and so the Times was my breakfast read. So I remember the outrage and astonishment on reading the article in the finacial pages recording the cancellation of P8. We were a Rover family (Grandfather foreman of the experimental shop, father a Rover apprentice, and neither had ever owned a car that wasn't a Rover!) plus the writer of the article had obviously been very thoroughly breifed by very senior disgruntled of Solihull!
I also remember the fuss accompanying the launch of P76 followed breifly after by the launch of SD1.
There is a compelling piece on ARonline speculating on the probable shared genealogy of these three cars. Having been involved in the development, financial commissioning and project control of capital plant I'd like to offer a few observations.
First off, the Australians contend aggressively that P76 is an Australian designed car with styling by Michelotti and that even the V8 engine is specifically an Australian confection and not a Rover hand me down. Yet if you read between the lines body engineering was done in the UK as was suspension development, both based out of Abingdon by Roy (MGB) Brocklehurst as his last job before retiterment. So have a look at the time line. P76 development starts in '69 after delayed go-ahead by the newly formed BL. in '71 P8 is cancelled and P10 becomes SD1 with the Rover and Triumph design teams brought together. At this stage you would expect P76 to be in early project definition, not yet ready for serious engineering to start. These changes throw up a completed set of body tools for P8 together with Spen King and David Bache oversight of P76 (and SD1). It'd be a shock if both didn't owe at least somehting to P8. And both P76 and SD1 launched in '76.
The P76 budget was tiny - which I suspect is something to do with why development took place at Abingdon. This tiny budget also gives a further clue - it implies relatively small tooling costs. So body commonality looks possible. Engineering wise P8 had a de dion rear end and double wishbone front suspension. P76 had classic Ford style McPherson struts up front complete with anti roll bar doubling as lower wishbone and a four link located coil sprung rear axle. On the face of it not a promising start for commonality.
So what do I think happened? Well the two key pressings in a car are the floor pan and the door inners or frames. P76 floor pan is the right size to be derived from P8 but the suspension pick ups at both ends are completely different. Interestingly SD1's peculiar torque tube axle could have used exactly a set of de dion pick ups! SD1 was developing in parallel with P76 so we could assume that the two front suspensions are closely related and probably share the same mods to the P8 floor pan. I should say here that small mods to a pressing are reasonably easy, changing the perimeter size or serious changes to the profile are not - I once had a spell in the press shop at Luton. But I've never seen a diagram of P76's rear suspension so can't say how compatible it might be with the P8 pan. The doors are a dead giveaway though. Comparison of photo's of P8 and P76 in my view make it pretty well certain that P76 used the P8's door pressings. And the doors and floor pan together dictate the overall shape of the car, so other pressings are likely to be usable too. But if that's the case where does Michelotti come in? Well he was doing a lot of work for David Bache at the time and I can imagine a commission along the lines of "see if you can freshen up these P8 pressings for Australia without spending too much money".
The final clincher for David Bache's involvement is the P76 Force 7 Coupe. Compare the photo's of this with David Bache's Rover P6 coupe "Gladys" - th aborted Alvis GTS. The P76 could be the office juniors lunchtime stretching and flolding project of the "Gladys" pictures on the photocopier! Judging by photos of the P76 interior only a died in the wool Marina enthusiast could have done that! So that probably was Australia? Mind you the steering wheel looks suspicially like one of David Bache's "Quartic" efforts!
And what about the engine? Surviving phots of P8 show it labelled as Rover 4000, and I've never heard what I think sounds like a convincingly definitive narrative of its intended engine line up. My memory says it was going to have 4.4, but I could be confusing the two cars. But Rover had surely been working on big capacity V8's - the Range Rover would have needed one by then too. Perhaps what really happened was that Rover shared their thoughts and prototypes with Australia and Australia production engineered it?
So is P76 son of P8? I think not. The concept of the two cars is miles apart. But P76 definitely uses lots and lots of Rover P8 bits and lots and lots of Rover brain power.
Chris
PS if you imagine the photo's of P76 retouched with those twin headlamps faired in and a single moulded lamp behind, the front end suddenly looks astonishingly like Gladys and the P7 prototypes!