I get all my oils from an oil dealer locally in 5 Gallon pails--Kendall for engine oil and Phillips 66 for TO4 equivalent oil for transmission---deliver right to my driveway

I use hydraulic oil ISO 46 in my hydraulic systems--i think the ant foam and anti wear additives make the Hydraulic oil a bit better

the reconmendation from caltex(chevron) is delo gold 15w/40 in all these old cats. in the engine and the hydraulics.
in the hydraulics and transmission (non hydrostatic only) you can also use textrans tdh which is their universal tractor drive line and hydraulics oil made specifically for case ih cane harvesting machinery which are all hydraulic driven. note all tractors with auxiliary hydraulics made since the 60s draw the hydraulics supply from the rear axle housing. it is a 75w80 gear oil and a iso68 hydraulic oil.

Im a firm believer in not using engine oil in gearboxes. none of which need detergent oils they need oils with anti wear and EP additives instead.