[quote=@TwilightDragon]
I might make him Poseidon
[/quote]

Well...

[quote=Fate/Stay Night]"That's not possible, Ilya. The Holy Grail can only call on heroic spirits, and you don't need the Holy Grail if you can reproduce phenomena on the divine spirit level."[/quote]

That said, it's of course your RP so it's up to you, but in terms of Fate mechanics it wouldn't work. ;-;

[quote=@Flamelord]
Anyway, pretty sure part of the rule of Heroic spirits is that they have to be dead. The Norse Gods are weird because they can actually be killed. Greek Gods, not so much. 
[/quote]

They have to be dead, they also can't be full Divine Spirits period. If they were Divine Spirits they'd need to have become non-Divine Spirits before kicking the bucket, like Fate/Apocrypha's Chiron. Avatars of Divine Spirits (Aspects like Fluffy Tail), partial Divine Spirits, or downgraded Divine Spirits (in the Chiron sense, not the Elemental sense) are all fine though.