Interesting, here's my latest crib sheet for the bottom part....
Rough-clamp part and align long edge,
Drill two 12mm holes - one in small hole location and one in centre of big bore,
Machine the counterbores.
Flip over to front side, realign the long edge and bolt down on some spacers thru the two 12mm holes into tee-slots,
Drill the three holes,
Mill the centre slot,
Mill the profile,
fit clamps outside of machining area and remove the two bolts,
mill the big bore
mill the small bore
mill the slot
In my mind it should work, I have kept the same work origin, the part was aligned each time accurately, no sub plate was needed just a couple of scraps.
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