I have resolved this one, seen sense and reason eventually.
I was becoming frustrated at a total lack of progress with my Berlinetta build. I do not feel that BW 65 auto boxes which have laid about unused for 23 years are a viable basis for a build. The car was last licensed to the end of Feb 1992. Auto boxes can be problematic at the best of times but with the potential for hardened seals, cracked or swollen 'O' rings, age hardening and embrittlement of other bits inside the box, I felt there was a high risk of issues developing within days of putting the car on the road.
I do not have the budget to rebuild an auto box. I was baulking at putting a lot of work into a build with the high risk of premature failure built in. So given I had a perfectly serviceable 'A' series engine and gearbox from my Roadster, it seemed a good idea to install that, at least in the short term, to kick start the project.
I placed the 'A' series unit in the Berlinetta and it fitted well enough, in a corner of the engine bay! LOL It looked lost! I calculated and weighed the car and it appeared that with the 'A' Series unit it would only weigh just over 600Kg 'on the road', which was slightly lighter than when it was in the Roadster @ 650Kg on the road.
However, I looked at the gearing and available power, it would need a much lower final drive than the 3.44 which is in the car. I asked around for a local source of a Transit diff, and was pointed to a couple of chaps who had axles lying about, they were all the wrong type, front loading, rather than rear loading. That led to somebody who had a big collection of engines, gearboxes and other stuff. I was offered a transit 2.0 DOHC engine with an MT75 gearbox, which seemed a good alternative, however he stopped answering his 'phone? I then followed up a couple of other leads, MT75 boxes and Mondeo engines which seemed a good, cheap, reliable and available option.
But, I really wanted my Rover V8 lump. In the pouring rain I called at a local breakers yard I had previously never heard of, I enquired about a Rover Manual SD1 gearbox. I was sent to a remote corner of the yard where there was an SD1 front end mechanicals assembly. V8 engine, LT77 5 speed gearbox, and front suspension, wonderful! They must have lain there for at least 2 years, there were trees growing through it. The gearbox looked like it might be OK, but I didn't give the engine much of a chance. It was the gearbox I needed, so I did a deal.
New Marlin V8 engine
When I got the engine home it turned over OK so did the gearbox, which also seemed nice and tight on the engagement and shafts. In with a chance, I drained the oil from the box and no signs of water. So I stripped the engine, which to my amazement is close to perfect inside. Despite being open to the elements with one missing carb and no air cleaner, there was just one cylinder with one ring seized. There is slight water marking on that bore (#8) but no pitting, so I am a very happy bunny. All it needs is cleaning, a few gaskets and re-assembling. I freed the ring by immersing the piston in boiling water and gently working it loose. All the shells are perfect, the cam followers and the rocker gear are as new.
The gearbox is now sitting in position where the BW65 box was with a 'dummy' P5 block and heads, I need to make slight adjustment to the mountings to retain clearance because the castings are a bit different but otherwise it's a straight swap.
My weight calculations indicate I should come out at about 750Kg with the SD1 unit, and the 3.44 gearing looks OK, so I am happy again!