Some Math for You.

Found it. According to my 1972 - 1979 Chiltons auto Repair Manual:

Bore x Stroke
Buick 350 3.8 3.85

Chevy 350 4.0 3.48

Pontiac 350 3.8762 3.75

Olds 350 4.057 3.385

Guess they couldn't make up their mind

Pontiac 400's and Chevy 400's were also dimensionally different.