What percentage of change is considered artistic license vs. a clone in video game development?

What percentage of change is considered artistic license vs. a clone in
video game development?

I'm a "weekend coder" developer making mobile apps and games and I've had
the desire to make my own version of a game made for the Commodore 64 back
in the early 80's by a small publisher e.g. Not EA Games or similar.
The game hasn't been ported / released on any platform since.
I want to make my version because it was fun to play but I can obviously
create much better graphics now (the original had 8 colors at most, and
requires a good imagination to transform a character image in the game
into something with 4 limbs and a head).
Since it will take effort to make from scratch, and the game will be
different when done I'd like to charge 99 cents to users... But I have
fears of being sued should the original developer pop out of the woodwork
from somewhere.
Here's a breakdown of original vs. My game intentions.
Original game was a 2D side view game (think original Mario bros) with 3
screens that flipped when you crossed the edge. You could collect items,
there were AI players that "chased" you, ladders, and some ride-able
objects... All within a specific theme.
My version would also be a 2D sideview, but be a sidescroller with at
least 3 but maybe 4 or 5 "screens" worth of content. Images would be all
original, have a nice 3D look to them, full color, shadows and lighting
effects. You would still collect items but they would be all different,
and you'd still get chased etc. but I'd try as best as possible to make my
game unique... and of course it would have a different name.
To a video game enthusiast that played this game in the early 80's they'd
be able to proclaim..."oh man this game reminds me of __!" I don't think
they would declare it to be a "ripoff" or "just a clone" though.
Are there documented cases where a developer has been sued successfully
for copying another game?.. And if so just how close was it? Likewise is
there a statute of limitations?... This game is pushing 30 years old...
Or is the answer just build it and see?