Interesting scenario. But you have TWO languages to consider, if you are basing it on the Norman Conquest. Remember, there was Middle English AND Anglo-Norman French.
Middle English eventaully became modern English, and, while Anglo-Norman French is basically extinct as a productive language, it did have about 300 years of vitality on the British Isles.
1) the state of
as influenced by the conquerors (of which you do speak to )
2) the state of
(i.e which regional dialect(s) did the would-be conquerors speak? By the late 1500's, I would presume an early modern variety of Castilian, but one needs to check further.)
Since "Spanglish" is used more for the modern (20th century) mash-ups of
spoken around the world, maybe call this "Spaniel", "Spañolés" ?
For similar contact phenomena, you want to at least chequear
the Llanito tongue of Gibraltar, the Spanglish of Argentine Brits, and the Spanish~Crucian creole spoken on the island of Saint Croix.
An interesting scenario, to be sure.