Re: 390 stroker block prep question
Sounds like a CYA story, but as long as he is willing to fix it, sounds like it'll be OK
If you know all this stuff, forgive me for the book, but trying to give some options
The reason I don't like his story is because measuring the pistons in the block is a bit goofy. He should have squared decked it to the mains and met a spec, measuring a rocking piston in a crooked deck is not precise, but CnC machining of parts today is generally a bit closer. Not all machinists do that, but that's what we do to blueprint something and make all corners the same. Most FEs tend to be all over the place.
Now doing BOTH (calculating and checking) isn't bad, as it makes sure your new components are what you think they are, but I haven't seen any in modern parts.
I'd recommend you calculate yourself before you go any further. Barry's custom Mahles are designed for a 10.160 deck, regular Mahles are designed for a 10.155, Probes are 10.155, and if he cuts too far, you'll be fighting deck clearance. Most 445 pistons are designed for 10.155 decks.
To calculate your required deck height, first calculate the stack height of the reciprocating pieces, piston, rod, stroke. 1/2 of stroke (2.125) + rod length (6.70) + compression height (depends on brand and design, get off the piston box)
That number is likely better than measuring it in the bore if your machinist can hit a target, and in a perfect world, that number = the number he square decks to
If he cannot square deck to that number, or has to cut more, then see how far above deck the pistons are, and pick a head gasket that gets you to no less than .037 and preferably no more than .050.
That being said, IF it ends up too short, Felpro 1020s are .041 and could handle pistons that are up to .004 above deck, and a Felpro 8554 (blue gasket) can handle pistons up to .014 above deck.
Example of pistons above deck - calculated stack is 10.160, he cuts to 10.155. You are .005 high, Felpro 1020 gasket is .041, that's .036 clearance, that is right on the edge (but could be run with a low RPM engine). Felpro 8554 is .051 thick though, so subtract your .005 and you are at .046, which is right on the money for a street/strip motor
Example of pistons below deck - Stack is 10.155 and he cuts to 10.158, you are .003 low, add the Felpro 1020 (.041) and you get to .043, perfect. In this case, the 8554 would be .051 + .003 = .054. That is OK for a stocker but I'd go Felpro 1020.
70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.