Hi Peter, I have an identical set-up to Warren's with the Dakota Digital box, the speedo reading is simply a question of calibration. Surprisingly out of the box it wasn't very far off. What a great piece of kit this box is. You simply make up a long wire with a button on the end and go for a drive with your GPS. You can then choose whether to have a really accurate speedo or "go long" by a few percent, I went with 3% but I tend to use the GPS speedo anyway.
The cooler is more of a concern for me because it is regularly minus 10 here and the box would otherwise operate for extended periods too cool. I'm thinking if you are commuting at all then this is going to help warm-up quite a bit.
Your selector gate is very interesting, you've added stops between the lower gears? Can you describe how this works? Perhaps you'd be prepared to supply a copy for a suitable sum? Or at least a PDF so I can print and stick to some metal to Dremel myself one.
Really if someone can produce a reasonable, complete kit and come in between £1500-£2000 then frankly I think for a car that's really used in modern traffic, you'd be out of your mind to put back a BW35 or BW65. These were only just about adequate when new anyway. The way I see it as a practical car the P6 only has two real flaws today, the gearing and wind noise at speed. Let's face it roads have changed a lot since then as well, not simply motorways but bypasses, trunk roads all require higher cruising speeds, which is where many classics fall down badly. I know the originality thing but unnecessary engine noise is just tiring and annoying. It's also out of character with a large V8, so if anything I think of it as therapy to fix a character flaw....
I'm trying to forget the actual cost. Shall we say really very decent P6 money? At the end of the day I still have a very average but solid car but this and the engine upgrades are about making a fun drivable car, it doesn't need to have perfect paintwork.
I just sourced the components and did very little of the work myself as I don't have a garage. This is unavoidable currently and had the box decided to fail at another time, I would have loved the satisfaction of DIYing more of this. However that would mean mothballing the car for this year at least and I don't know when I'll have so much time to drive as I will soon. Also the guy I contracted to do this is an absolute perfectionist and I now have what I can only describe as the Roll Royce of brackets merely to locate my radiator expansion tank when a simple strap would have done. Seriously, when the bill came back I probably would not have done this, at least in this country and the costs implied. My fault, I should have agreed stricter terms when starting the project. I thought providing the major components and the write-up on AROnline would be enough to come in with a realistic estimate. Err, no. I think buying Andy's box and the crossmember then the rest is well within the ability of anyone who can change a gearbox but boy, does making-up custom brackets and general fettling eat up time.