318 into /6 '74 valiant sedan

It would be less complicated to not have a classic car at all, so if that’s your argument why bother?

Part of having a classic car is working on it. While there’s nothing wrong with a /6, upgrading the car to a V8 will improve it’s appeal and value. And make it more fun to drive IMO, which is the whole point of having a classic to begin with. A 4 door /6 car is pretty much at the bottom of the value-for-originality scale. They’re literally donor cars for most folks, so anything that improves the value and drivability of the car is a win in my book. Why discourage that?

All true. Unless it is a total survivor slant car, original EVERYTHING< perfect,,, the slant cars are at the bottom of the collectability pile. Stock?, yes lacks a bunch on power. But as you know some of us enjoy it for what it is. Years back, I would have argued what is the fun in any small block??? But that was before the stroker. Stock 340? I had way more fun in a stock 383 4 speed Runner with 3:55 or 3:91 gears , and the 440 cars and occasional hemi car. It is all relative.
This subject has ben argued till it is like beating a dead horse. There are purists that hate anything not totally stock right on down the line to every thing has been customized.
Easier to leave a good running slant, but lke said, many in or hobby love to work on them. You can sit down and roughly figure all the costs in changing it over. Most parts have been listed. Me I always have several cars, from slants to something faster, sometimes OEM, sometimes I changed it over. It is the hobby.