Let me ask a question about cylinder walls

[CRZN427]

The original 289 body that became the test mule for the big block car had a 390 for fitment, since the basic outside dimensions of the various FE big blocks are the same.

I don't believe that any of the "427" cars actually had a 390 from Shelby.

If you put in a stroked crank you will have to concern your self with different rods since the longer stroke will push the stock piston above the deck.

There were three stock stroke dimensions for the FE blocks.

3.500 for the 352 (4.000 bore)

3.780 for the 390 (4.050 bore)
3.780 for the 406 (4.130 bore)
3.780 for the 427 (4.230 bore)

3.980 for the 410 (4.050 bore)
3.980 for the 428 (4.130 bore)

There was also a 332 CID FE '57 and '58 but my book dosen't list that displacement.

My first Cobra had a 390 and it performed quite well.

If you are going to be concerned with showing every one else your clean rear end then you might as will get on with the dual paxton 427 like Shelby did. By the way, he found that an automatic made the dual paxton 427 drivable.