Both. Contrary to what I have been told by the many experts, the telescopes DID NOT go back to Enfield during the conversion programme. They went to 3 or 4 of the big workshops with dedicated Instrument sections and were converted and IF NECESSARY, repaired, in a what was called a WORP or War Office Repair Programme.
Sterling Catterick, Warminster and Aldershot were the usual ones but Bovington was another who workshop who did a few.
I don't think 27 or 43 Command milled a slot and engraved but I have seen a couple that would seem to contradict this. Warminster were guilty for re-engraving the new deesignation BELOW the old designation where it became illegible when assembled to the bracket. Later when the spec was clarified, they re-engraved to the norm of ABOVE the old designation. That's why you'll occasionally see the new designation engraved twice!