[SAJ]

Thanks a bunch guys. I re-arched the spring before all the replies were in. I set the longest spring to plus 1-3/4 inches of arch as per Columbia’s suggestion (on the basis that if a little bit is good, too much is better!), I then reshaped all the other leaves to fit this longest one. But when I bolted it all together, to my surprise the re-arch of the whole assembly was 2-1/4 inches more and the length between eyes 29.1 inches.
I put it in a press and loaded the spring until it was the max length attainable in the car between perches (31-5/8”), and when unloaded the arch had settled to 7”, or 1-5/8 more than before, which is close to Columbia’s suggested 1-1/2 inches.
I put it back in the car at this and refitted the perches as is, with moly on the tapers and copper/lead antiseize on the shank and nuts. They seated well.
The car now sits with plenty of shackle clearance and slightly more on the left than the right.
It is still a mystery what was wrong unless both springs had low spring rates, as Fordors suggested. I believe I was taught years ago that when a spring is reset cold above its yield point the rate actually increases ( for small distortions ). Can a spring expert comment on this?
Maybe I have just compensated for some other unseen problem. The axle outside the perches does seem to “sag” in the photos as Tim suggested, but when looking at the car itself it looks OK.
The shackle was in backwards for one photo because I knew it had to come out again, and every time I went under the car to fit the plate on the back someone called me out again. So I just threw it on from the front temporarily.
You guys are Eagled eyed for sure!
I will fit shocks, cotters, brake rods etc tomorrow and road test it. I hope this crude, cold spring reset is a permanent thing.
Thanks to all who helped and Ryan for providing such a wonderful information resource.
SAJ in NZ