What small cam do I have???

Does it have a compression release on the engine….?

 

Somewhere in the last 38 or so years a block may have been "windowed" or an owner may have had a "freshened" engine sitting on the floor at just the right time.

 

Look on right hand side for piston coolers or just the bosses for them to be drilled. The rectangle cast in patent tag on the left side of block tells me NHC 250-855 block. They were the last of the old round water pump blocks to be used before the suitcase style wp came out. Also the last blocks to use the tapered crank snout. NTC350 or anything after 1972 will have flat snout crank. The 12-x-71 is the casting date. The after cooler is late NTA 380 early NTC350. Looks like when it was remanned the compression release rod and bell crank was pulled out and holes were freeze plugged. Common upgrade as timing and compression would be changed to not need it anymore. Cummins also did it through their recon program.
Keep in mind the 250-855 block was the same as the 270,290,335,380’s just no turbo. The 350, and 380 was the first with the big after cooler and piston coolers.