.

 

Can't help you with the bolt size for the housing, but as a word of caution- if you use steel bolts and you probably have a factory (or aftermarket too for that matter) aluminum intake manifold, you want to use antiseize compound on the threads. I made the mistake of removing and reinstalling the thermostat housing bolts on my '84 305 once without compound and when I went to remove them again a few years later found that the threads had seized. Snapped off the heads of both bolts- wound up having to have the holes redrilled and tapped......