I agree, I don't think most buyers really worry all too much about matching numbers. 10's of thousands of muscle cars out there missing their original engine, and likely will never see them again.
Nice to at least have a correct date coded replacement but again I don't think it's all that critical. Once the original engine is long gone, just having a correct replacement type of engine with the right components on it is enough to satisfy most people out there. It still feels and drives like a DZ. Most important in my eyes is just having the foundation, the fact that it's a "real" Z is getting to be a real challenge to find nowadays, let alone worry about the drivetrain. What I'm sick of seeing is Z28 badges on every Camaro ever made, and worse, people trying to pass them off as such.
Nice car, if I were on the market with that kind of dough, I'd buy it.
Could look at it another way, there are a handful of "real" Z's I've seen forsale, some with original engines, some questionable. I'm talking cars that need full blown restorations from top to bottom. Owners are wanting $35k or more for a car that needs completely restored.
Ask yourself, How much would it take to completely do a frame off correct type of restoration to the level of the car in this thread? This car isn't even what I would consider concours quality, but a very nice example. Just some rough numbers, but lets take into consideration the people out there that have to sub out everything. Paint and body work....$20 to $30k?? There are shops around here that won't even simply spray a car for less than $10k. Taking it down to a rotisserie and doing it right?? Most shops charging upwards of $100 an hour labor?? The total amount of parts and pieces to buy is immense. Want NOS stuff?? Even good quality reproduction will nickel and dime you to death. When done, you can easily surpass $60k to $75k investment when you're paying $35k for a car to start with. Those sellers don't want to admit it but it's reality for most people, and most likely why these cars are forsale in the rough shape that you see them in.
Even at $75k a car like this starts to look like a bargain. Still kind of spendy for a 69 Z in my eyes but restoration costs add up quick. I'd spend $75k on a car like this before I'd spend $35k on one that needs completely restored. Plenty of others at a lower level of restoration in the $50-$60k range as well. Just a different way to put things in perspective.