Dave, I spoke with the lady at Hitzer yesterday and we discussed the 983 vs. 503.
She mentioned that the 983 has a huge firebox (3.5 cuft), which obviously shows consideration for woodburning. I don't believe that it is an "EPA" woodstove, but it obviously can do it pretty well. It has been made for 13 years and looks like it was designed as a coal/wood combo stove. They're in IN, so I can imagine that wood would be a good back pocket option. From the limited amount of info available, it also looks like it takes a little bit more experience to burn it well - compromise quirkiness.
Your 503 is a new design. (I found that the old hitzer website is still online and its not mentioned.) The lady mentioned that the 503 can burn wood if you remove the hopper, but it has a very small firebox so it's borderline practical. It is done. Does that idea look reasonable to you for the May-Oct time? I'd like to be able to take the chill out w/o going to dino fuel.
(My apologies for the newbie Q's and hijack, but once you consider coal, it's a slippery slope. "Why don't we just get a stoker furnace?" You're pulled in trying to fill a fireplace/windtunnel with something useful and wind up shovelling coal in the basement.) -Charlie
PS - Just to end on topic, I'll get the restrictor if we get the 503.