I'm thinking I want to upgrade to a 261 for my truck and have read posts here telling what trucks they came in but my question is how do I positively ID a 261 cu. in. motor? I'd like to know what I'm doing before I go shopping.

1945 Chevrolet G 506 1.5 Ton Military 4X4
1967 Jeep Cj5 with 283 SBC