They have to be an interference fit by 3 to 5 thousandths depending on size. They are installed by sweating them in. Heat the block & freeze the seat to get it started. They will generally drop right in if the temps are right. Dry ice is the best way to freeze them.
This link is about heads but there isn't a lot of difference except the block is more troublesome to heat up than a cylinder head is.
https://www.aa1car.com/library/ar993.htm