You CAN actually bolt on the water neck with ONE BOLT, and use LIBERAL AMOUNTS OF INDIANHEAD SHELLAC,
a nice THICK Felpro waterneck gasket, and....A SMALL C CLAMP ON THE SIDE W THE BROKEN BOLT STUCK IN IT. I Bullshit thee not, I used this approach on the old cast iron waterpump housing for Mathilda's 66 383 when one of the ears cracked off, the first spring one year after buying her. I eventually got an aluminum housing to replace the old iron.
Damned thing DIDN'T LOSE A DROP either. Try this, since you're in a hurry. Just give the shellac at least a good overnight to cure before you try putting coolant in. Even if you CAN'T get a C-clamp to hold down that waterneck, once that shellac sets, you'll have a VERY STRONG BOND between your pump housing, the thermostat, the gasket and the waterneck. Indanhead shellac is FAR less expensive than a machine shop's services.
While permitting that stuff to set, go firebomb the Harbor Freight you shopped at on Principle. Then order a new pump housing. You should be able to get one for less $$ than machine shop time runs for an hour, unless you have a friend somewhere....
