I doubt with this build your engine builder cc'd the heads and measured piston top to deck distance. He would have charged you extra from a typical rebuild for those services.
But I'm guessing the head and deck were just minimal cut for clean up of .004 each and the 4 valve reliefs at 5cc total. And that X heads are typically 72cc measured. The Sealed Pro 428 has a compression distance of 1.829 in. with is theoretically .007" above a perfect 9.6" block deck height...With all that I get about 9.55:1.
If the 4 valve reliefs equal 10cc's it 9.06:1
Still, you could try backing of the timing a couple degrees and see what happens.
Yeah it was a not a fancy build but it did receive attention. Here's what I know from notes.
I found some of the notes I took during the build, sorry I don't have some of the specifics and it was over a year and a half ago.
The block had been decked and line honed previously so as you say we just ran it through a deck and line hone to clean it up a bit.
The heads were milled for clean up also so good quess there too.
The rotating assembly was balanced.
Along with the 428P we installed the following bits
Hast rings 2m694 .040
Bearings CB-481P std/ms-963P std.
Lifters Comp 822-16
Pushrods SBI 190-1450
Stock rockers and shfts
Felpro 260-1121, .039 head gaskets
Flatop Piston 428P, .025 in the hole
Stock x Heads with cleanup, , 68 cc
Stock valley shield
Let me know if that helps with the calculation, let me know if that changes anything.
... he just texted me back and said he recalls it being closer to 10:1.
I will try to pull some timing after I swap the heater hoses and rig a recovery tank and change the cap.