Google of the part number led me to the same conclusion as Overk1ill on the application.
A cross for the Donaldson P551268 would be a Wix 51515, Motorcraft FL-1A, Purolator L30001, Hastings, LF115, etc.
The Donaldson P550776 looks to cross to a Wix 51334, Purolator L14459, Motorcraft FL810?, Hastings LF402, etc.
For educational purposes only
Originally Posted By: OVERK1LL
And here we go:
Equipment: KUBOTA L2250DT
Equipment Type: Tractor
Engine: D1402DL
Donaldson:
P551268:
Lube Filters Product Attributes
A - OD (Inches): 3.67
B - Thread Size (Inches): 3/4-16
C - Length (Inches): 3.39
D - Gasket OD (Inches): 2.83
E - Gasket ID (Inches): 2.46
Product Type Description: LUBE SPIN-ON FULL FLOW
Primary Application: KUBOTA 1732132430
P550776:
Lube Filters Product Attributes
A - OD (Inches): 3.15
B - Thread Size (Inches): M20 X 1.5-6H
C - Length (Inches): 3.15
D - Gasket OD (Inches): 2.48
Anti Drain Valve (Y/N): 10-15 PSI
Product Type Description: LUBE SPIN-ON
Primary Application: KUBOTA 7000015241
Those are all the Donaldson filters, including air and fuel, that show up for that Kubota. That was reversing the given product numbers to give a tractor model that they corresponded with and then putting that tractor model into Donaldson's system.