The V-8 Ford flathead had three main bearings, same as the majority of British-pattern undersqare four-cylinders. In fact, the classical inline Euromotors generally had two crankshaft throws twixt each main, i.e., 3-main Fours, 4-main Sixes, 5-main Straight Eights, etc. (Packard reportedly built a one-off inline 12)
For pure flexy weirdness, early '30's MG J-2s used TWO mains for a four-cylinder crank.
, and Duesenberg Straight-Eight SOHC racing engines in the early '20's had 3-main Straight-Eight. Harry Miller copied Duesenberg's lower end design, but his DOHC 4V head breathed so much better and made so much HP that the cranks were doing evil catastrophic things...to his drivers. (Who needs a roll bar?)
Dodge/Chrysler/DeSoto/Plymouth flathead I-6s all had four mains, as did Ford's flathead AND 223/262 I-6s (indeed, so did the 144/early 170/200).
Some of the Straight Eights had five mains, some had NINE.
Odd-fire V-6's run two rods on a throw, same as modern V-8s, only four mains instead of five; Even-fire V-6s run offset throws, four mains, which sorta puts them halfway in the four-main I-6 mode
The bench race still goes on: bearing speeds, frictional gains/losses, torsional rigidity, harmonics, skinny girls v. full-figured...
Eddie