Here are the dimensions for the Roadmaster Adapter Kit for Blue Ox Motorhome Mounted Tow Bars, part # RO64FR.
pin size = 3/4"
pin length = 5"
measurement from inside lip to the end of the pin = 4" view full answer...
The total width of the # SP501L ladder is 12-3/4 inches. This is the outside measurement of the step pads since that's the widest point. The actual dimension of the step that's usable for your foot to land is about 10 inches between the uprights. view full answer...
I attached a picture that shows the mounting hole dimensions of the Flow Max RV Fresh Water Pump part # LC689052 that you referenced to compare to what you have now. This mounting pattern is a standard size so it should fit what you have but you'd want to check to make sure!
I attached a review video for this pump for you to check out as well. view full answer...