Looking at the Gulp JigHeads, Berkley probably developed the best-holding Collar for that odd water-based Plastic. I would try to, #1, imitate what Berkley did by finding a similar Collar. 2, find a suitable Mold that has all the options (weights and hooks) I need, and 3 (if You really found the right mold), find one that can be used for other Baits, Rigging, Applications.
If I were fishing Gulp and wanted to pour my own 'Heads for it, looking at what Berkley did, I think I'd get the Poison Tail...
http://www.barlowstackle.com/Do-It-Poison-Tail-Weedless-Jig-Molds-P264C56.aspxOne mold has down to 1/8 oz....
Takes the KILLER Mustad 91768 but there's also an optional Hook with the 28/30-degree Bend but without the Wide Gap (if You wanted)...
The Poison Tail can be rigged MANY ways...
That Collar is versatile...set Your Mind Free...and it's similar to the Gulp Head Collar...
Weed Guard can be omitted when the Head is poured...