The Master Parts Manual indicates that your dipsticks and tubes may be correct. Note that the note by the dagger says that the tube should be shortened for pre-1955 jobs. The note does not seem to differentiate between 1st and 2 series trucks. Does your 261 have the fixed or floating oil pickup? The type of oil pump and pickup may determine what the oil level in the pan should be. When I installed a GMC oil pump with a floating pickup in my 1954 261 I made a lot of measurements to ensure that I had the correct length tube for my dipstick.

Hoyt

Hoyt