I see that ATNS, the South African ATS provider who are contracted to handle St Helena's aeronautical info, have now published the charts and other information regarding the airport. It is at
ATNS: AIr Traffic Management
(or search ATNS St Helena project).
A couple of things stand out - the runway 20 VOR/DME procedure is presently "intentionally blank" - I wonder if the VOR is still considered a bit unreliable? There is also a comment that its range is "severely limited" from 210 to 010 degrees - obviously the effect of the terrain, but I'd have thought it might be OK at cruising altitudes.
The other interesting thing is that there is a separate DME associated with the Localizer (i.e. 109.3MHz paired with DME channel 30X). This means that pilots do not need to tune in one frequency for the localizer and another for the other DME which is co-located with the VOR.
There is no NDB/DME approach to runway 02 - only an RNP one. The NDB must be quite a powerful one as its range is quoted as 200nm.
No mention of GBAS apart from it is annotated on the aerodrome chart - there are four positions marked which maybe the GPS receiver locations (although I am surprised to see them so close together).
Various notes mention "Severe turbulence may be experienced close to terrain on approach" - not surprising for this cliff top location.