I don't believe it was a war time only deal.. unless we were at war in 39. The sheetmetal .040 steel sleaves were finally dropped and replaced with the .090 cast iron sleaves as they wore better. Same reason also why they went to 3 ring pistons instead of 4 ring... too much extra wear.
Many people have the block bored for the cast iron sleaves when replacing the sheet metal ones... though i *think* you can still get the .040 ones from places like Dennis Carpenter.
Also.. virtually impossible to know what type of sleaves you have till you pop it open... even if the sn range is a steel sleave.. you never know who has been in it these last 50+ years and may have swapped them over o the .090 cast iron sleaves.. or bored and fit custom sleaves.. or even ran it bare with OS mercury pistons.. for a few more CI at the expense of their block..
Soundguy