Despite soaking those stubborn snapped studs in "homebrew", there is too little of them left sticking above the surface of the block to grab onto with a tool and back them out. For all I know, they'd come out now, but I got nothing that can grab onto them strong enough to turn.
I met up with my retired 911 buddy who is an accomplished machinist/welder/hobbyist to have a look at them.
He's taken my block back to his place for a couple of days to see if he can get them out. He figures he's got a couple of options to remove them and preserve the threads. I've told him to take his time and get to them when he can and he promised to be careful. Now that he sees my dilemma in person, he understands. He's the type of guy who likes a challenge and I have little doubt he'll be successful.
Time until takeoff
Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.