Cool those bolts are good for over 400.

M12 x1.75 is the tap you need. Also check the head bolts don't bottom out in the threads measure bolt in block distance between washer and block face. then measure head which should be near std size 139mm if not skimmed.

Its been mentioned to look at brass bung in head (sorry Paul) but sometimes these have been knocked in further to give the wrong impression if you know what I mean

Regards