Got a big block says 7.4 on the side,how much can I bore this block

Should be able to bore .100. But a sonic check would be beneficial.

Aside from the testing. On some of the older blocks, you have to pay close attention to the internal rust scaling under the deck surface also.
Look closely at all the threaded deck holes.



Seen some that sonic ok and still had core shift.

It's always a crap shoot on older blocks. They were mass produced and a lot of them.