I'd cut the pins off internally. Mark the centres of them on the outside, then drill through with a 50mm mag drill. Insert 40mm pins, check and weld. Easy enough.
spot on other than drilling/broaching through with 40mm (typo Doob?) ... exactly what I would suggest too ... see no issues at all ... you have enough of the 60mm hole edge showing to be able to get an accurate centre mark in the cut off stub ends.
personally, once you have accurate centres marked, I would put a 4mm hole through the 60mm pin stubs, to centre the broach pin on, then build up the recessed hole flush, with weld, around its circumference, to get a face on the outer face of the cheeks at the 40 diameter, then broach it ... can then weld your new pins on the outer face of the cheeks, making them way easier to remove in future, instead of the welds being recessed into the cheek plates