Block is machined to accept the oversize sleeve and sleeve is a press fit into block.
While there are different types of sleeves whether they secure from top or bottom.
The sleeves for typical Model A Ford application are a straight sleeve and need a step in bottom of block to be held secure.
Contrary to one poster on this site saying that there isn't heat transfer through the sleeve and engine will run hotter isn't true as the sleeve is same material as block.
Looking at pictures I've posted shows the work. Once sleeve is installed very hard to see where block begins and sleeve ends.
http://www.jandm-machine.com/cylinderBoringSleeving.html