Not directed at you Ralph, just furthering the train of thought...
Also block to flywheel clearance, input spline engagement, spigot bush placement/length, ring gear engagement to starter (mentioned), clutch adjustment (mentioned), rear main seal to flywheel clearance (it looked pretty close in the picture), bolt hole depth after machining, bolt length.
Basically everything that comes into contact or near to the flywheel should be measured and checked.
Most of that should be fine but all should be checked.
1mm might not matter but 5 mm would likely be a different story. It has to be checked.
Did I mention that stuff should be checked?
Would you really want to use a spacer that produces possibly different expansion rates than the flywheel and crank and in turn changes bolt tension and stresses the bolts and dowells more than the already problematic setup?
Adding another element that can slip and wear itself and other parts is far from ideal even if dowelled.
Is manufacturing a billet custom hardened spacer (to allow for somewhat even thermal expansion of said spacer) worth the cost of just replacing the crank?
Would anyone reading this be happy to leave their car at a shop and pay for or allow this kind of fix?
Not me, no thanks.
If I had to be dodgy I would just remove any runout then partially tig the bolts to the flywheel once they were torqued up but I'd prefer to do it right the first time....oh wait.....
Who knows maybe it will all just stick this time with just being put together as its?!