Whilst it does not appear to be a Wiseco piston (usually have a W marking on the inside) it does have the L shape (dykes) top ring which was common for Wiseco (blue box) in the early '70s. The number on top is 60 thou the equivalent of a 1.50mm oversize (65.5mm overbore) Rings for this piston may not be easy to find. The carbon on the side skirt is commonly known as blow-by indicating some wear to either the rings or the bore or both. You would need to have the bore measured accurately to determine if it is within serviceable limits. I don't think they made an 80thou oversize piston kit for this model
As for the oil in the cases a leakdown test would confirm if a seal/gasket or case damage is responsible. This requires assembling the engine, sealing the inlet and exhaust then pressurizing the cylinder to monitor any pressure loss. Not exactly an easy job without the right equipment. It's a little hard to say which way to go without seeing the engine but Matt's statement of the donor motor may only be in need of a top gasket kit, a set of rings (if available) and small end bearing to save splitting the cases maybe the go. As kdx Geoff said..it all depends on how particular you want to be.