That’s the question. My cougar is in great condition . Very solid body and I believe the sides of the car to be original paint. I can tell the top surfaces have been painted and blended. It has several door ding dents on the sides of car and a couple in the hood. Under the hood appears to be clean but original other than valve covers, intake and oil pan have been painted. Interior has been changed to black from the original Ivy gold. The gauges are showing there age and the dash lights are dim. The chrome appears to be original and showing its age.The car is supposed to have just over 40,000 miles on it and that’s listed on the title,but I am not sure I can confirm that. I like a nice straight body with shiny paint and clean new looking dash and gauges. I would also like a 4 or 5 speed transmission. Should I leave it as is or make it what i like.
My 2 cents. Leave it stock as much as you can. Or just make sure you leave it in running condition. As SOON as you make it undriveable, that’s when it starts SNOWBALLING. Please don’t go down that path. Off MY soapbox I leap!!! BTW Beautiful car!!!
Do what makes you happy without worrying about what some future owner might want is my take on your situation. Other than the change of transmission, nothing you noted is anything other than restoring your car. Gauges can be cleaned and bulbs replaced with LED (great change BTW).
For what it’s worth, changing my 1969 from 3 speed manual to a 5 speed manual is one of my favorite modifications.
Also, the change to a five speed (in my case a TKO) requires no cutting or welding so if you wanted to hold on to the original bits for some future owner to reinstall them that’s an available option.