How were 32-bit minis built in the 70s/80?

[Warren Toomey]

I'm building my own 8-bit CPU from TTL chips, and this caused me to think:
how were 32-bit minis built in the late 70s and early 80s? In particular,
how was the ALU built? I know about the 74181 4-bit ALU, and I know (from
reading A Soul of a New Machine) that PALs were also used.

Did companies get custom chips fabricated, or was it all off-the-shelf chips
with a few PALs sprinkled in?

Thanks, Warren