Unfortunately.........
............. Low Ball, the pair of Wessex you saw in the river were not Mk 5s but Mk 1s and they were put there on 12 Apr 65 as a result of a mid air between two 845 cabs. There was only one survivor - a petty officer aircrewman, who released his running harness and dropped into the river, as I understand it.
The RN lost three men and the army lost a Para Regt patrol and one or more 'attached' soldiers. If you are a member of the Malaya & Borneo Veterans Assoc, they have a roll of honour with all these guys listed.
A chum of mine was at Nanga Gaat this very March and he photographed, inter alia, the remains of the engines and some other bits which still remain and can be seen depending on how high the river is.
Furthermore, you ought to be entitled to the Pingat Jasi Malaysia (PJM) - a medal issued by the Malaysian Government which the (very rude) British Government didn't want to accept but then relented, although not for wear!!! (So who's going to enforce that bit of useless legislation??).
O-D