That's precisely the year/engine car I'll be looking for someday soon.
It depends entirely on what you want to do with the car. If you're simply looking to have fun, as Tim is, then a "matching numbers" car isn't that important.
It is unlikely you'll ever find the correct engine. You might find the correct block casting, but each block was stamped with the vehicle's VIN at the factory. You would have to find the very engine that came out of the car.
Cars that don't have the original engine are valued at far less than original cars, although I've been watching the available cars, and the sellers these days don't seem to believe that.
Just a factoid to consider. Like I said, if you're looking for a fun car and don't care, then a non-matching car is just fine. And there are many out there.
However, if your goal is to restore the car to the highest quality, then you just can't start with a car that has the wrong engine. It'll never be up to the top standards no matter what you do to it.
Hardtops are fairly difficult to come by, but not impossible.Will not be inexpensive, but nothing like a Bentley or Jag.
On that note, the car likely has a "build sheet" taped to the gas tank, unless it's been molested or in an accident and lost. If you're restoring the car to the highest standards ("NCRS"), then adding a top to a car that didn't originally ship with one doesn't merit the cost. It won't help the judging. If you're out for fun, then by all means pick one up. However, most of us would never drive the car when a top was required.
I personally debate interior color with myself all of the time. Both the interior and exterior trim are indicated on the trim plate, located on the driver's side inner fender (you'll see it when you open the door...by the dash). I don't care for blue, red, silver, or white, but if the perfect car came along ($$$), would I change it? Probably not, speaking personally. I like mine original. But Tim is definitely considering a different color, according to his restoration page. I think it again comes down to: is the car for fun, or for restoration to a high standard? If for fun, go for it. If a restoration and you want authenticity, you'd swap back in the original color components. If NCRS quality, that'll be a tough thing to do as you'd want to find quality (actual) components, not reproductions.
So if I were you, I'd ask myself what I want to do with the car. Bottom line. Personally, I want authenticity, so I'll be picky. It'll cost more, to be sure. But I owned a 1970 before and want that authentic feeling again.
Only you can answer that question for yourself.
Best of luck! I'm envious...wish I had one myself. I do miss it.