First off, you don't have to double post mere minutes after just posting.
Well, depending on how you want to go about this, you could just call this a project that's inspired by Castlevania instead of being a Doom version of it. If that were the case of being a project inspired by that game series, people likely wouldn't be expecting it to be like that instead of how it currently is with being designed to be similar to it. Wow, I wonder how well that sentence came out... Anyway, I think if you're gonna go by the route of "port of Castlevania to Doom", you may want to drop the guns. It's not like you still can't be focused on ranged attacks. Look at Heretic and Hexen and how you can still shoot like any FPS even if you're using magically objects instead of firearms. In the very per-alpha screen shots you posted, I could barely tell the pistol was suppose to be one till I looked at it in a certain way.
Well, Castlevania is more known for platforming and close range combat, but having ranged weapons shouldn't be too bad proven that feel like they fit in. Again, I think you could save yourself the trouble of "it's not like Castlevania" and still keep the theme going if you go the "this is inspired by Castlevania" route and avoid using any of it's characters and other stuff unique to it. On a final note, I do agree with dropping the current story with the UAC having some connection to the Belmonts. That just blows my mind and not in a good way either. Still, it's ultimately up to you what to do, but I'm just giving my thoughts on the matter.