I bought mine cheap knowing I would have to tear it apart. The original plan was to drive as fix as you go. That did not work out. I am currently 5 years into a full frame off. I have $45k worth of parts in the garage. Zero labor $. Now I am rebuilding every single piece on the car, all by myself. This approach is not for most. But these are 50 years old. And I want my car 100 percent reliable. So with lesser mechanical skills, costs will rise, my advice is buy the best condition car that you can, and fix little things as you go. Ultimately the 454 big block will cost more, be worth more, and be much more unique on the street. Gas mileage is pretty irrelevant for an occasional driver. The engine itself is still probably the most reliable part in the car, even after 50 years. If it runs good, don't mess with it.
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Even if it checks out good, you may still find you need some significant dollar repairs shortly. Even the best ones need something. So just be prepared for that.

Driving one of these on the street attracts so much attention, like a show car. The body shape is timeless. Enjoy it.

 

You asked for opinions, so here’s mine: buying a C3 (or any classic, for that matter), with the intention of having someone else work on it/restore it, is a mistake. Unless you have plenty of disposable income.
Watching those dollars flying out the window every time something breaks or needs maintenance will put a damper on your enthusiasm very quickly.
Also, once you do have a fully restored beauty, total reliability is still somewhat of a pipe dream due to the quality of replacement parts these days. If you restore every part you can (following expert advice and methods) instead of just buying new, you can control that quality a bit and increase reliability.

I’m running an unrestored ‘71, and if I didn’t have 40 years of experience working on my cars, and had to send it to a mechanic, there’s no chance in hell I’d be able to afford to keep it in the road.

 

It is a point that starts to show. First of all, the BB has been the reason I considered this C3 in the first place. It also motivates me to keep the car in its original condition (although the lack of modern comforts such as parking sensors, airbags and more supportive seats will be missed - this is Europe after all). A 50-year old car is never maintenance free, I get that too. This car will indeed require a substantial upkeep, but my main concern remains the condition of the chassis frame, suspension and various supports. From the reactions I have received till now, it is clear that I would benefit most from a model that has already been subjected to this process at some stage. Yet, if multiple owners have been passed, retrieving that information might prove nigh impossible. I have already contacted a person that owns a car shop and has years of experience in restoration works. He shall accompany me to check up the car, and his advice should provide decent feedback. I am definitely not interested in restoring a vehicle from scratch, which is why I only considered those in running condition, although I do respect those that take up the challenge ;-)
You mention not to change anything on the engine if it runs. I was under the impression a full revision would help avoid breakdowns caused by aging parts or failing gaskets, or how do we call it: preventive maintenance ?
I really appreciate your input on your experiences with the BB. Something tells me I should not let this opportunity to own one slip away, despite the investment is will prove to be.
Undoubtedly I will need your, and this forum's, support in the months and years to come, to help me understand how to properly take care (and repair) this scheduled new addition to my carpark.. :P

 

Believe me , it is one of my concerns. I'm not stupid, and will certainly learn a thing or two from owning a classic car, but I cannot say I enjoy working on cars. Love to drive though ! As one without prior experience, I will have no other choice than to have someone do the maintenance for me during the first years, hence again the importance of purchasing one in good condition. And honestly, any hobby related to cars is ever cheap... much to the dismay of our wives :-D

 

Just to confirm I have been watching those recommended YouTube vids and really happy I did. Although not being much of a YouTube fan, both references have certainly enriched me. Thanks a lot !