Thanks! 
Unfortunately work on the mod has stalled, instead I resumed work on another one (not Doom or GD related at all). But the idea to make a GD style weapon has not been abandoned yet. I think the easiest and fastest way would be taking a crossbow from Heretic or Hexen and turning it into Runebinder’s Spellthrower or another GD crossbow. But I’d rather do dual-wield pistols or a rifle. Either way it’s gonna be a lot of pixelart work, which for me is pretty time consuming so it has to wait until my current project is done.
edit: thinking about it, I could also try to screenshot the weapon in GD via Grimcam 1st person perspective 