261 Strato-Six (nice name).
The 58-62 USA truck 261 has a full-flow oil filtration system. These engines are identified by their large (1/2" NPT) oil-line holes in the block. The factory oil filter for these engines was an impressive canister (with cast aluminum top/cover). I understand that a by-pass style canister should not be used with these engines.
The Canadian Pontiac 261 engine used a by-pass oil filter for all years.
Tim
