Broke thermostat housing bolts

[IowaZR-1]

Yep! I done did it!! Was looking everything over getting ready for the trip to BG next week and spotted a little leak coming from around the thermostat...started draining it and I twisted off 2 of the 3 bolts. I haven't touched the 3rd one yet as I'm leaving it in(one of the mounting bracket bolts) so I can drill out and retap the broken ones first (surprisingly there is a clear shot to drill them) and with any luck #3 will come out. My question is.....what is the size of bolt....all I have to go by is the twisted off heads. I need to know diameter and pitch of the threads. Anyone ever don't this before, any helpful tips? Thanks!