Yes it looks like a 41 99 "Mercury" block. 239 cubes. 60 thou over = 3.248" so it's probably 60 over.
Please heed the warnings not to hold the block like that, there is a current thread running which shows motors that have fell off the stand damaging the bellhousing area.
The motor is similar to the one I am currently working on, (yours has slightly later features). You might find some of my videos helpful, for instance I feature stud removal in some of them.
https://www.youtube.com/channel/UCzc...ro40j-vjjZShg/
Mart.