Ebay has cat 40 spindles, you will most likely need to grind em and put in new bearings. Pretty much every spindle I watched for had the spotted syndrome on the taper inside, I'd say go for it, I wanted to make an actual mini mill, small travels like 19x14x20 xyz, I already have some parts but switched gears and cnc'd my knee mill
You can get t slot tables on ebay too, one from a brother tap drill machine would work nicely.