What I should have said earlier was that 'some' of the early Mark 1's were fitted with wrap around front sights, not all. It is thought that these wrap arounds were left over from the Model 150. All Mark 1's were fitted with plastic triggers initially, but due to breakage a lot of these were replaced with metal triggers.
As Danny 'Garvin' states, an in depth thread about the above can be found in the archives.
http://www.airgunbbs.com/showthread....ap+front+sight