[Barry_R]

Don't want to upset anyone. But Ford did not turn 390s into 428s for service. You occasionally find a 391 truck block that'll go to the 428 bore, but they are not the norm by a long shot. Some service blocks were apparently 391/428 castings that could be machined as needed - but they had 391 features like the big distributor hole and the compressor oil return passage. Most .080 over 390s are ebay specials that'll split a cylinder wall somewhere down the road. Could last hours, weeks, or years - no guarantee.

The 428 has a different water jacket core and normally has the numbers "428" cast into the floor of the jacket either below the center freeze plug or visible looking straight down through the front and/or rear coolant opening on the deck. Anybody buying one that knows their stuff also knows this and the price will reflect that inspection. The 428blocks are in high demand for the Mustang market.

A 427 will outpower a similarly equipped and sized 428 or 390 pretty much all the time. The bigger bore equals better breathing. No question about it. If I am building a Cobra for myself its gonna be either a max effort 427+ racer type of deal or a 390 based sunny day cruiser. I think the 428 is a great middle ground selection - but I am not much of a "middle ground" guy