I'm thinking of replacing the cranks on my 80's falcon road bike, the left side crank arm rounded out and right now i'm riding with an old mtb crank on that side.

I'd like to replace with something close to the original which was a 170mm Stronglight, I've actually found one on ebay in france for $30 plus $16 shipping

I also did some searches for campy sets and found some that looked pretty nice...
VINTAGE CAMPAGNOLO ATHENA CRANKSET EXCELLENT

What should I do? I would like to stay original but i'm kind of leaning to the campy...

Also Should I/will i need to replace the bottom bracket?