I found a picture of a 5C/4205 on my computer and it looks a bit different to the adapter shown above. The new boost gauge is central within the plate. I found this auction on Ebay which may give more details.

http://www.ebay.com.au/itm/RAF-AIRCRAFT-UNDERCARRIAGE-INDICATOR-ADAPTOR-PLATE-5C-4205-/171348617706?pt=UK_CPV_Aviation_SM&hash=item27e52c69ea

I’ve seen this type, but it is the earlier one (6a/700) that was used on my panel.

Bob T.