if the vin near the oil filter matches the cars vin, would not that indicate the Motor is true to the car ? Everything else proves out x77 z28
Yes, in instances like this, I tend to disagree with others.
That is of course if you are certain we are looking at a real Z. For this scenario to work, for me, it would have to be a Norwood car with an X code for starters. As long as you are certain it has a legit data plate and is original to the car, hasn't been tampered with, and is an X33 or X77 then we can be fairly comfortable it's a Z. Other tell tail signs would help as well. As long as the vin tag is also original and untampered with, and lines up with the build time frame, then you're off to a good start.
From there, really the vin at the oil filter would be enough to confirm it's the original block, as long as you're certain that vin is original and untampered. At this point there is enough evidence you are looking at the original block. If all that checks out it wouldn't scare me a bit and would have little affect on value in my opinion. The deck stamp isn't the "tell all" and they are frequently messed with, but it's certainly nice to have if it's real. What saves a car like this, in this instance, is that Norwood was thankfully stamping vins at the oil filter by this time frame. Otherwise all would be lost.
What's interesting is that this process has been used to verify LOS built Z's that have no X code, by verifying the vin at the oil filter matches the car LOL. Sort of reverse prognosis. So to say it's not a viable means of verification on an X code Z is a bit odd.
Decking the block isn't that uncommon. Many were done back in the day when these cars weren't worth much so it's not unusual to see. So many of these engines (all models) have terrible deck surface heights that very several thousandths front to back, side to side, some blocks are actually twisted. Doing a proper rebuild almost always includes "squaring" up the block after align honing which means sometimes a light pass on the decks to sometimes taking off several thousandths.
Then you can get into the "zero" decking scenario where builders want tight quench for better mixture motion, fends off detonation, makes more power with less timing required etc.... Some move piston pin heights, some deck the block, or a combination of both.
