The grooves were cleaned thoroughly, with a ground off old ring end, and brushed clean with a brass brush.

Isn't carbon buildup on the groove sides the more serious problem that will result in broken rings, than buildiup at the bottom?

The extra spacer came with the scraper ring (marked #2) and was for fitment at the bottom of the groove, not along the wall.

The cam timing issue I am still considering. Since I am reusing the cam and lifters, which showed wear, although minimal (It had been replaced at some time, silicone sealant at the bottom of the cam cover), I don't think a degree of timing will make much difference.

It sort of a crapshoot, I realize, but the main purpose of rebuilding this engine was to correct a low oil pressure condition, which turned out, I believe, to be caused by the melted front cam bearing. It was a very smooth engine before.

The rings and bearings and new oilpump were preventative. I ran the oil pump with a drill to prefill all the galleys with oil. It seems to have reached them all.
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MPergiel, Elmhurst, IL '74 145e T-5 'Orange Alert'