Apologies for the delayed response - I have been waiting for approval to borrow a couple of bits of information.
Sumary of the changes:
Barrow Road crossing has been replaced by barriers. These are still controlled by the crossing keeper with the signals still slotted by Oxmarsh. The barriers on the up side block the line to New Holland Pier.
All of the main running signals at Oxmarsh have been replaced by new semaphores. The up direction signal protecting Oxmarsh Crossing blocks the line to New Holland Pier. The down direction distant has been replaced by a reflectorised board. The up direction distant and the various subsidiary signals remain the same. The new signals came into use on Monday 29th March 2021.
At Goxhill, all signals have been replaced by colour lights, with AWS protection on all signals (I think previously this was only present for the distants). All are still controlled by Goxhill box. The signals in the down direction were commissioned at 18:00 on Sunday 21st March, those in the up direction at 18:00 on Monday 22nd March.
The previous newest semaphore signals on Network Rail metals were Dudding Hill Junction signal DH12 and Neasden Jn signal NJ2R, the latter a distant. Both are on the same post on the down (westbound) Dudding Hill line which links the Midland Main Line at Cricklewood with the Western Division of the Southern at Kew and the Great Western at Acton.