I can't afford to buy this at the moment but just in case I have a change of heart what would you look for - super briefly - to figure out the condition of a LS diff?
The market for the ex works race car is probably about right, given what it is and is unrelated to the market for 'ordinary' Sprints. Although I don't know the UK market, i suspect there are a few of the higher priced ones there that are well overpriced. However, like most classics either a low mileage unmolested original in excellent condition, or a well restored car with great attention to detail will command top prices from those who can afford it. In NZ the top prices paid to date are around $15000-16000NZ, so around the UKP9000 mark. One that requires a full restoration including removing rust though would be unlikely to fetch much more that 4-5000NZ, even if it was currently driveable.
LSD
You don't need to buy a complete axle to get an LSD. Just fit one to your own axle. Buy an existing axle and you should budget to refurbish the LSD and the rest of the axle. That assumes you can find parts. Personally i don't believe there is any reliable way of determining how worn the C&P or the LSD are without at least stripping it down, given it isn't in a car.
Philip Lamour in Sydney (Sprintparts) had a batch of Sprint LSDs made in 2003 and I had one of those at one time. Don't know if he would have any left. Also I know 3J Driveline in the UK advertises it manufactures new ones. I've used some of their products before in the racecar and the quality is very good.
If you buy a new one then you also have the potential to change the diff ratio with the crownwheel and pinion to either a 3.77 or 4.11 ratio using those in the diff of an early Triumph 2000 saloon, manual or auto. In reality you only need do that if you are racing on the track. Then you would need to consider what preload, then what ramp angles you want as these can bestow different characteristics either braking into a corner or accelerating out, as the LSD is working in both situations.
The other question of course is why do you want an LSD? I don't believe it provides any material benefit for a road car unless you are driving very hard on twisty loose surfaces.
Beware the folk that wrongly think all Sprint axles carry an LSD; They were only ever an option, and not one that was commonly taken up. For an LSD you should look for:
The axle casings were originally painted red
The axle number stamped on the underside of the casing will have an 'S' suffix
The wheels will rotate in the same direction when one is turned if an LSD is fitted
...but casings can have LSDs removed, and standard axles can be welded to mimic one, so the only real way to check for LSD is drop off the rear cover and have a look inside
