The Spencer Carbine

[vintage hunter]

Lately, i've been feeling an urge to go into the Post-Civil War era and the Spencer Carbine has drawn my attention

I was thinking of going for one of the reproductions that shoots .45LC.

They're a bit pricey, IMO, and like you've said there isn't a lot of info available on them. Have you considered a Springfield Trapdoor? With a bit of patience you should be able to get a nice original Trapdoor rifle in 45-70 for about half of what you'd shell out for a repro Spencer, and on a good day an original TD carbine for the same or a tad more. The 45-70 Trapdoors in good condition are normally very accurate and are fairly cheap to feed, especially if you re-load.
It's also possible, for the most part, to get a Remington Rolling Block in good shootable condition for about the same or a bit less than a Trapdoor rifle, but, depending on caliber they can be expensive to shoot and/or get set up to load for and some are finicky about ammo. I've been considering an 1879 Argentine myself.

Just buy a Winchester of the caliber you wish and warm it up...

Easier said than done.