Thanks for the warm welcome, no pun intended.
Yeah, I 'figger learning to burn coal in this unit will be about equivalent to reducing my Phase 2 EPA special (by "Country" recently sold by Lennox so I hear to whom I dunno) wood stove from an 8 to a 6 inch pipe going into a 35 foot chimney in the basement. Try warming up THAT flue!
Matter of fact the Vigilant 1a will vent into that very hole! Yikes.
But no, the throat pieces are actually two brackets that screw together or maybe just set against each other that come off the bottom of the hopper to supposedly regulate the flow of whatever sizes coal you choose onto the grates. They fit into one of several slots in the inside of the hopper, depending on what size you're burning.
As Vermont Castings dispensed with the entire hopper assembly in the Vigilant II, I guessed that an experienced person burning coal might be able to make do without a hopper and just burn as is done with a Vigilant II, in layers. The grates are pretty different however. And from what I've been reading, several people do like the hopper and some don't even think it's that bad an idea. I have to admit I do like the grate design in the Vigilant 2.
If I could come up with a good way of getting heat into the ductwork I might stick with a radiant heat source as I like that warm-to-the-bone feeling and so do my pets. Hooking into forced air ducts with an auger feed, thermostatically controlled does have a certain appeal though.
I now have two coal kits; one with a fair amount of use with no throat and another essentially new. I don't think $75 is a horrible investment for something I could maybe get $400 for. And hey, I could restore one off these things to museum quality! But going through the hassle and expense of casting iron for something obsolete probably wouldn't prove too fruitful. Bad enough I took a hit trying soapstone as firebrick in my wood stove. That cost a few bucks and though it might work in the VC, no way it's happening in a Phase 2 stove without a 30 mph wind outside.