I have a Kirkham Motorsports Cobra. Interestingly, David Kirkham describes this car as a "hybrid". This is because it has the 289 slab-side body but the 427 Cobra frame and suspension under it. Best of both worlds, if you ask me- the better handling and braking of the bigger Cobra, but the prettier looks of the original 289 design. KMS cars are very well done- they are built in an old aircraft factory in Poland that the Kirkhams bought and converted to use to build race cars. Mine has a built up 302, about 350 hp, and a Tremec TKO 600 transmission, which is the best shifting manual box I have ever used. It shifts like a rifle bolt- really precise and easy. Come out and see it sometime.
Today, at long last, I got to drive my 280SL complete with Getrag box. After the "incident" with 85-90W gear oil in the transmission, with which it would barely shift at all, we drained that out and put in Dexron; quite an improvement. I drove it about twenty or twenty-five miles today. The new ratios are much better. I actually think that 1st is still a bit low- I think it is 3.46 in this box, and about 3.20 would be better, moving the other ratios up closer together as well, but overall it is quite livable. I have not gotten it up to highway speeds yet but all indications seem to be that at 3000 revs she will be doing about seventy, which is fine. It is a distinct improvement over the original four-speed.
Speedy Cables finally came through for me, and we found the proper BMW fixing screw to hold the speedo cable into the transmission. We also had to remove the yoke and send it off to be sleeved, because its' sojourn outdoors whilst it was not in the car had pitted the surface which seals against the pinion seal. It seems dry now.
The speedometer seems fairly accurate, although I have to check it with a GPS or iPhone. As long as it's close I'm okay with it. The tacho needle jumps around and will need to be sent in to Palo Alto Speedometer this winter. They did the clock on my 6.3 and made a very nice job of it with new internals and stock appearance. I recommend them. I do NOT recommend that horrible outfit in New York who did the Smiths gauges on my E-type- they charged a fortune, and they came back no better than before. Nisonger, that's the name. I wouldn't trust them with a rectal thermometer.
It's been a long road to get to this point, but the car is nearly complete, and I am very grateful for the help and advice I received here, without which this would have been impossible- and even more expensive, for less results. Thanks again to all, additional info to follow as I get some miles on the car.