1963 Mercury Meteor Custom - Opinions needed

Greetings folks,

I've come here for some advice/opinions. I have recently found a '63 Mercury Meteor wagon. Mercury only made the Meteor wagons in 1963. That makes it a rare one. The original owner drove the car daily from 1963 to 2015 when he passed away. The car is an excellent survivor car. It's completely original except for the carpet, engine and transmission. It seems the owner, in 2013, had the original 260 V8 and two-speed automatic replaced with a matching numbers 289 and C4 from a Mustang (reason unknown). From what I have read, that was a common swap if something went wrong with the original drive train. That's where my question comes in. Being a rare wagon, does the non-original engine lower the value of the car? Or, since it was an upgrade, does it increase the value of the car?

All advice and information is appreciated. Thanks

Here's an example. Not the actual car.

 

If someone's looking at it as a collector investment, the upgrade will lower its value. If the original drivetrain was kept and was included with the purchase, the vehicle could always get restored back into its original condition.
This is critical, because Meteors sold so bad that 1963 was its last production year, accounting for only 7480 wagons:
https://www.mercurystuff.com/1963-models/index.html
It was probably upgraded, after a major engine repair would have been more expensive than to just swap the drivetrain out for an engine that stayed much longer in production than the short-lived 260 which would have had a harder time moving that wagon with its two speed automatic and smaller displacement. Or maybe the owner just wanted more power, if there wasn't anything wrong with the original drivetrain

 

I don't think it hurts the value of the car at all. I'm not sure it increases it a ton, but I'm sure a 289/C4 is a much more desirable combo than a 260/2 speed. While the model itself is relatively rare, I don't think it is necessarily collectible because of the specific drivetrain. If the original engine and trans were some rare high performance combination I might think otherwise, but I wouldn't let a non-original engine and/or trans keep me from buying the car.