If I recall rightly the issue with the Belvedere avpin was that on a mis start the fuel could gather in a u-bend ,resulting in a double dose on the second attempt and an explosion. At least one aircraft lost it's back end in the subsequent fire and another lost the front end so both were cannibalised to make one good one. Westland then made up a spare nose section out of of another crash, caused by a double engine close down in error , but it was never needed.