I checked ring gap by pushing a couple of rings in different cylinders, in turn. All rings I measured were around the maximum spec, either just over the limit, or just below. Too big a gap I can live with and I decided to leave well enough alone. Here's how I measured
It looks like I initially installed the piston rings wrong.
The pistons I bought came with 5 sets of piston rings, whereas the car came new with 4 rings per piston. The Haynes manual and the shop manual were of no help (well, see below). After I received the pistons, I gave them to the machine shop that worked on my parts, so they could balance everything. If there was a sheet of instructions when I gave them the pistons, there was'nt one when I got the parts back. Oh well.
It may now be appropriate to mention that even if I have rebuilt of couple of engines in the past, I've never worked on British machinery, and 5 ring pistons are something I did not know existed, and had never seen. But, with the power of the internet and the collective wisdom available, it appears a mistake may have been caught before it could bite.
So, the rings are as follows:
The rings that came labelled 1 and 2 appear to be identical. Here's a close-up.
The third ring is stepped and has a small "top" printed on the wide side. The step can barely be made out in the picture below, and the marking is out of focus, but this ring is clearly different.
Here's the one that is was throwing me off. It came in a little bag called "oil ring", and it is made up of four parts, as can be seen. Initially, I could not get it to fit in the fourth groove, so I gave up and put the oil scrapper there. Then Cap'n Bob (On the Yahoo bugeye list) suggested I was making a mistake, and I noted a sentence in the Haynes according to which the middle portion of the ring should be fitted first. (I have two different editions of the Haynes and the reference to multi-part rings, and to the assembly sequence is not in the earlier one).
So I tried the following: the flat component of the ring (third from left in the picture) is shorter than the others, so I reasonned it must sit at the bottom of the groove - I put that in first. Then the wavy component (second from left), then the top and bottom components. Lo and behold, I got it to fit.
Here's what the four components of this ring look like:
Finally, here is a picture of what I call the scrapper ring. It came in a little bag labelled "5", and I figure it would then make sense to put it at the very bottom of the piston.
So, below is a piston I put together in this fashion. I've done only one so far, and hope I will be able to get confirmation that this is the proper sequence. Note the step in the third ring, the scrapper at the bottom, and the fact that the flat component of the fourth ring is not visible, it is buried under there. This is how the piston looks like, Sunday evening, March 30, 2003.