I've finished the crank spacer:
Spacer machine down to size, about 17.90mm with in 0.1mm of the original.
Cam belt pulley test fit, this a very tight fit so it will need the "the tool" to get it back off again.
As the M52 crank nose it a bit longer than the M20 the washer in the front doesn't sit flush.
Washer in the lathe, need to take about 1.25mm off giving 0.1mm space between it and the crank nose.
Finished off and the edge smoothed off
Test fit of all parts on the M52 crank.
Comparison: M52B28 crank and the front and M20B25 at the back