Bottom Bracket
Parts
J&L/ZTTO Ceramic Bottom Bracket 30mm Italian
Beware! These don't thread in smoothly and may damage your bottom bracket threads.
Bookmarks
Component Weights - Damon Rinard
Vintage parts weights.
Sheldon Brown - Unthreaded Bottom Bracket Cribsheet
Table of non-threaded bottom bracket sizes.
Wheels Manufacturing - Bottom Bracket standards
Table of bottom bracket standards
Klein Problem 1
Shows Klien's unique bottom bracket, talks about Klein bike history/design.

https://jimlangley.blogspot.com/2008/01/q-klein-pressed-in-bottom-bracket.html
Klein bikes from the 80's/90's have 2 press fit bearings and a square taper spindle.
Consider just removing the bearing seals and re-greasing instead of removing the bottom bracket.
You can try knocking out the spindle with a hammer (support the frame with wooden blocks).
*Mentions a Reset Racing tool, but I can't find it now.
Articles
Cup and Cone Bearings
Bicycles have used cup and cone bearings in rotating parts for generations. Nowadays many parts are replacing them with sealed bearings, which are less servicable but entirely replaceable. Cup and cone bearings are easily maintained, but if parts wear out can be difficult to replace.
Maintenance
Fresh bearings are packed with grease, but over time moisture and grit can work it's way in. Bottom brackets and wheels can pick up serious dirt that can increase wear on bearings and races. Service bearings periodically to clean out dirt and replace fresh grease.