Re: F Spaced pickup or Standard for neck of RG550
F-spaced bridge pickup is wider then non F-spaced humbucker because Fender tremolo's string spacing is wider then Gibson style bridge string spacing. ( Fender spaced - F-spaced).
And neck position humbucker is usually not F-spaced, because neck string spacing is narrower then bridge string spacing anyway.
Actually, most people( in Seymour Duncan forum for example), think that there is no difference in sound between F-spaced and non F-spaced humbuckers. It is matter of string alignment with pickup poles. (And you can have blade pickup with no poles)
So in frankenstrat Van Halen put ordinary non F-spaced pickup in bridge position, ( there were not F-spaced pickups back then),
and Steve Vai, if I remember correctly, has bridge F-spaced pickup in neck position.
So there is no rule, just look for sound you like.