Wider front tires help steering and handling. 70 aspect ratio tires are wider than 80 aspect ratio. The number is a percentage of width to height.
If it were me, I'd get a set of 6 all of the same size, if for no other reason than if you have a flat front tire, you can swap it for a back one.
You could get a set of 245/75R22.5 tires, they'd fit with no problem.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.