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You typically only need Fender spacing for the bridge pickup, so a P90 in the neck would be fine (which IMO is normally the best place for one). I've just measured a P90 against the neck position of one of my Teles and it's spot-on, whilst at the bridge position it's about 2mm too narrow.
Simon is absolutely correct in what he says above with respect to the wire gauges and resistance etc.
Maybe these are what you really want - https://www.seymourduncan.com/pickup/p-rails-set
Another left field suggestion but you could always put Toasters or Filtertrons in it? That'll give you something different.