Managed to get some more time on the car today and focussed on drilling and tapping the 3 broken studs. All were sorted with out too much hassle and much safer than risking easy-outs. Learnt my lesson there.
I had to get a new drill bit and tap set as I didn't own the required 'F' sized bit to drill a 5/16" - 18 hole, HomeDepot got me sorted. To make things easier I had to remove the thermostat housing and found a relatively new looking t-stat heavily stuck in place with a load of gasket sealer. The housing is pretty beat up and corroded so I've ordered a new one (along with a new t-stat) from RockAuto.
Now I've just got to deal with the one remaining stud and figuring the best way to get it out.
