Based on some quick research, the number you provide "3836330" correspond in the Chevy Master Parts Catalogs as a "Generator brace" Group 2.317 for 6 cylinder engines. Not a correct "GM Part Number" for the cam in question.
Some further digging (see screenshot pics below from the 1929-57 Master Part List Catalog) shows that for the '56-'57 6 cylinders in Commercial and Utility Trucks, there was a cam that has a casting number of "3836390". Is it possible the number you see on your cam is this one??? If you can provide a picture, it would help determine yay or nay.
Beyond that, the book does not describe the cam as hydraulic lifter or solid lifter. But, looking at the listing for the "Lifter" (tappet) data, the corresponding '56-'57 Commercial and Utility Truck selection indicates the use of a 2-piece solid lifter (not hydraulic). The only listing for hydraulic lifters refers to Passenger vehicle engine applications.
Others will surely chime in here with more details or info I am not aware of (not all info is found in just these books), but this may help answer your question.
Dan
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
