That would be great if you can confirm that the SD1 alloys are in fact hub centred, then the wheel nuts on the SD1 at least don't need to be accurate for the wheel holes as they are just clamping the wheel to the hub, and the rears will also centre on a same size spigot.
The more technical info we can get for this topic the better as it will give others the reliable info they need to choose what alloys they want to fit.
I purchased an adjustable reamer the other day and set it to the wheel nuts I got from USA and they fitted well to give a runout of 5 thou which is acceptable to me. Some of the nuts (about 4 of them) didn't fit as they were slightly larger than the reamed hole, but I didn't want to ream the holes to the largest size as that would make it loose for those with the smaller shank diameter, so I may have to buy another 5 nuts hoping they will be to size I need (may have to take a punt)
What kind of rover alloys does this car have, the series 1 style or the series 2 style, which is what I have?
As you mentioned it's definitely not a good idea to use the tapered nuts from the steel rims as this will just spread the hole potentially causing cracks to happen.
Actually when fitting the U.S. Sourced nuts I have a couple were found to get tight then loose as I was running them down the studs indicating that these also have concentricity issues, I mean, how hard can it be to machine the shank diameter then drill and tap the thread on a CNC lathe?? To give accurate concentricity, even I can manage this on a lathe at work, which makes me want to just buy some stainless hex bar and make up a batch myself to suit a 3/4" hole/shank diameter.
WINS is indicating that they have wheel nuts to fit the rover alloys to the P6 (to suit the 7/16unf thread) but I found out that what they have does not suit the series 2 alloys, maybe they suit the series 1 version as Graeme has on his P6B in NZ, which still needs confirming as to what size hole is on the series 1 wheels.
For the time being I'm having a bit of success with reaming the holes to suit the wheel nuts I have but just need to buy a few more to selectively have a full set, oh, and I need to shorten the shank length, which I can do at work, and the washers are ok size wise.
Even those who chose a non rover alloy such as minilites must have had then supplied with suitable nuts as a package which I understand that minilites have a 3/4" holes???? I read on the www somewhere.
The chap who recently fitted Jensen wheels to his p6 must have sourced suitable nuts to locate the wheels unless Jensen have the same 7/16unf threads as well??? Must drop him a pm.
Anyhow, I'm just rabbiting on now to keep interest in this topic to hit the 1500 views mark
Looking forward to what you can add Mike, cheers