I have a 1967 Case 580CK and from what I can gather on the forums is that the oil recommended at the time of manufacture was single weight oils. Are these recommendations still the best advice given the advances of motor oils over the last 50 years? The 530 manual indicates SAE 10W or 5W below freezing and 30W over 80 degrees. Can a multi-viscosity oil such as 10W-30 be used all year round?
yes, can be used,, a engine that old has wear on moving parts,, give time to warm up in cold weather,its not a space ship
My late 80's lawn tractor recommends both single and multi-viscosity oils with overlapping temperature ranges. Is there a reason to use one over the other?
Straight viscosity grades tolerate abuse better than multi grade oil. Sae 30 or 40 in an air cooled lawnmower is common. The Case does not abuse oil, and will benefit from modern oils, I'd run modern 15w40 diesel oil in it, and plug the block heater in for an hour before starting below 50.
I wish it had the cord for the block heater. Where can I find a cord for this configuration?
I've seen that male pin receptacle in many places, (Kat's Heaters) and think you can get a female plug to fit. Does your heater thread into the cylinder block, or is it clamped in place? The "hex" shown in your photo; I can't tell if that is the former retention nut for the cord, or the part you use to install the heater.
Before you spend money on a cord, test the heater with an ohm meter to verify that is functional. You can most likely but the complete heater new for a little more than a replacement cord will cost. Unscrew it and determine what size the pipe thread is of the hole. It is most likely 3/4 inch. When you get the old one out you will see what style the element is. They are available in different wattage ratings. They can be purchased at any auto parts store.
The big one is probably the ground, and the other two should show a low ohm reading between them, but a high/infinite reading to ground on the engine block. A person might stick insulated female spade connectors on the end of a cord cut off a junk microwave and stick the spade connectors onto those prongs, but then again that person would be taking some risks to do that.
I got a 70 ohm reading on the two side-by-side prongs. It's threaded into the block. There's no easy way to get on it to unscrew it with the loader frame in the way. I've given thought to making a cord out of individual connectors and a cord.