1968 Mustang convertible?

I own a a 1968 Mustang convertible with only 75 k miles.It has the original interior,carpet and original engine. I obtained a build sheet and the car is equipped with a 200 six with power steering,light group and a power top. The original radio still work.It also has the turn signals inset into the hood. I am wanting to convert it to a 289 V8 engine. How difficult is the conversion and by doing this would I destroy the value of the car? I know the six is not the most desirable engine.

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