As this is a rather unique collection of spares and difficult to value accurately even by the serious enthuaiast, never mind the 'armchair' ones - why not allow a one-off unique listing of all the parts and allow PM offers only for individual parts or 'lots'.
That way the BBS membership has access to a rarely offered hoard and the seller can get a true reflection of the worth of the inheritance...he also doesn't HAVE to sell them if he doesn't want to....

It's win, win for everyone and the poor chap at least gets the chance of a decent return....C'mon Mods you know it makes sense