Since you're looking for a shooter you might want to look at it from the perspective of how much would a new Armi-Sport cost?
New a carbine is going to be around $1400 or better. After you walk it out of the gun store its worth around $200 less,
after firing a few times knock off another $100 or more and by then you'll have invested an additional $350 or so in reloading gear and brass.
If you ever want to sell it. It's an Italian rifle made less than 8 years ago. It's value is always going down.
The original gun you are looking at will always be a real Spencer and if a good shooter then it's a prize.
If it's a sleeved gun with a 3 groove bore then it should be in 56-50. Many were sleeved and rechambered from 56-56 to accept the new 56-50 cartridge after the Civil war and shipped out West to fight the Indian wars.
The 56-50 is easiest true Spencer caliber to load for. Not a heeled bullet but inside lubed with a strong crimp.
One less special reloading die to buy and that is always a plus.
Brass is available at Buffalo Arms as is everything else you will need. If they are out or back ordering 56-50 dies check C4H custom dies online. That is who makes them for the original guns.
The gun at $1,000 to $1,600 if well cared for will always be worth that or most likely more. So what's to lose?
If you enjoy shooting these guns, nothing beats shooting a real one.