breezy, Can you take and post pictures of the codes on the engine itself you have provided? The block casting# and stamped Serial Number sequence seems to indicate a 1958 235. I think the block Serial# decodes as:

F = Flint assembly plant
1025 = October 25th (the letter I was used as the numeral 1 in serial number stampings)
J = 3100-3800 regular production

This is from the 1958 GM heritage Data file.

The head casting number may be a misread. If you clean and recheck, I think you will find it to read - 3836848. Agreed that the block casting date as you have listed doesn't make sense. I would also recommend further cleaning and rechecking. You may find the first character to be an L instead of a 1, which I think decodes to October = L, 3rd = 3, 1957 = 7. That late in the year would probably correlate to a 1958 model year engine.

Maybe Mike B can come along and confirm or correct what I have suggested.

~ 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)