Thread chaser size for 1990 5.7 ltr. head bolts

[72timemachine]

Hello,

I am replacing my cylinder heads and was curious to know what size thread chaser I will need so I can clean out the thread bolt holes on the block. I did search this site, however, I cannot locate the information I need and do not have a thread pitch gauge to measure the head bolts

Is it also acceptable to use a tap in place of a thread chaser?

One other question, is there anyway to clean the cylinder walls without scratching them? When the head gasket blew, some coolant in one of my cylinders left a film on the cylinder wall.

Thank you for any help.