I have an FE engine with 66 427 on the block (bellhousing side) with no casting numbers. Just curious because cylinders measure about 4.070 inches and I believe that is what a 390 is.

 

360/390: The bore is the same (4.05"), the stroke is different. 360 = 3.50" / 390 = 3.78."

 

Thanks, just curious about the 1966 427 markings and the lack of casting numbers.

 

Any chance it's an aftermarket block? Though 4.070 is smaller than I'd expect for an aftermarket.

 

Some drunk at the factory failed to swap out the mold pieces.
Look on the web for tips on identifying the possibility of this being a 428 capable block.
There is a 428 block for sale on the FeForum that has the 66-427 casting numbers.