I would agree 52k is on the high side with the other mods that are on it, and assume it is missing those original parts.
FYI -I have seen NOM 302 69Z cars sold in the 50k range though.
Whether that is a real DZ stamp isn't going to mae a huge difference in the value of the car since it isn't original to the car.
While getting tougher to find a real 69Z these days, they are still plenty of them out there for a fair price.
For this specific car there are so many Z specific details to check out to verify it, and verify what it has and doesn't have. YH wheels, exhaust manifolds, no vinyl top, black grill for starters. Each thing you find that is incorrect is a deduction in price/value. Just based off of those things and the replacement motor, I would say a fair price for the car would be around mid to upper 30's, and that is only (if is real) AND if the trans and rear are original to the car. Original paperwork would help.
Hope this helps.
FYI- don't use photo bucket, your pics will disappear in each post.