We have a Farmall 300 w/ narrow front end but it's been sitting at least 20+ yrs now. The reason for the narrow front end is when you get to the end of the row you can basically turn on a dime and get started right back into the next row. I've never used it much and mostly raking hay with it and has since become an ornament out in the field. I'm sure the engine is seized up in her. Someone had installed an Oliver loader and it worked good for clearing out the barn but then dad got the wild idea to make the bucket larger and had plates welded on to make it more of a scoop bucket but the weight was too much for it and wouldn't pick it up. He's since added a loader to our Massey 1100 which can handle it but also hard on the clutch.
I'd use an HDEO such as 10w30 or 15w40, depending on where you're at and if it's cold in the winter you could also use 5w40. I'm sure back then they recommended either sae20 or sae30 depending on temperature.