As you pointed out, we had 8 (80%) more divisions in '91. We hadn't had a draft since the mid '70s. Today's population is larger too, although I'm not sure the military age population is, unless you count illegal aliens.
We Could do it.
I got out of the Navy October 80 turning down $15K and next rank. In late 1982 I tried to go back in. The recruiters weren't interested and I had a good recommendation for enlistment and a good record. I may be wrong but as far as I know from the end of 1981-1989 the ranks were pretty much filled even on a Cold War posture.