Classic/Antique Car Repair: 1966 Mustang, Keep original?, car hobbyists, v8 models

Question
I have a 1966 Mustang.  It has the straight 6 200, a bench seat in the front, and only has 38,000 original miles.  I was thinking of changing some stuff but didn't know if it is rare enough to keep it original.  If not i plan on putting a 351 in it and doing a few simple other things.  Can you tell me if it's valuable as is or if I could go ahead with my changes?  Thanks.

Answer
First, I have to tell you I am not an unbaised person. I am in the hobby to preserve examples of the best original cars I can find, in as close to factory condition as possible.  

You are a very lucky person to have a rare and very unusual car there, with the extremely low mileage, and the 6 cylinder engine.  If you were to run it on eBay, you'd find a LOT of interest in it, just as it is.   If you modify the car in any way, you would join the hundreds of thousands of other early Mustangs that have been fiddled with and can never be considered original again.  ANYONE car do that to a car, but only a very few ever have the chance to preserve an example of an original, low mileage automobile.  

Another thing for you to consider is that the Mustang used many stronger parts in their V8 models, and putting any V8 into what was orignally a 6 cylinder car is going to get you into all kinds of handling, durabilty, braking, and other safety issues, and unless you are an experienced automotive engineer with the resources of an advanced design and testing facility, you are going to wind up with a very unsatisfactory ride - the 351 is even more likely to cause problems than the 289 which was used in the V8 Mustangs.

If you are interested in maximizing your financial gain, the best thing you can do is to have the car professionally detailed, then run it on eBay and sit back and let the true old car hobbyists fight over it - all you have to do is collect the money.   If you are interested in joing the old car hobby for the rewards it brings, just keep it, preserve it, maintain it, and DRIVE it! - drive it to cruise nights, car shows, Mustang club meetings etc. -  you'll meet some really nice folks who are like minded and you'll make some lifetime friends in the hobby.  

It's your choice - I know what I'd do, but it's your car, you get to decide.

Good luck, whatever you choose.

Dick