For what it is worth, I will attach the information from my service manual. It may or may not be readable. Nothing is said about how to protect the new seal from damage during installation.
I took a quick look at my 1170 and I see a double lip seal. I see the sealing surface is machined back so the seal could slip on another 3/8 inch.
In the cross section that I posted before, it appears the new double lip seal may have to slip over a sharp corner and not have a chamfer to help protect it. If there is a chamfer, my concerns about damaging the new seal are greatly reduced. We know for small implement wheel hubs, one can gently work and rotate the seal over a sharp corner. Obviously, this monster hub makes it harder to be gentle towards getting the seal over a sharp corner.
4435's post mentioned removing the entire unit and standing it up vertically. That should help align the seal lip as it approached the sharp corner. Also, doing it on a bench where one can observe closely the seal as it approached the sharp corner is helpful. A small, dull screwdriver or dull bent wire may be helpful for getting the seal lip over the sharp corner---and some grease.
If a horizontal assembly is attempted without a precision hoist, the taper roller bearing will likely not maintain good alignment for the seal because the heavy weight will tend to separate the bearing cup and cone. Even if there is a chamfer there may not be adequate alignment provided by the taper bearing if assembled horizontal.
All this considered, I would probably change this seal in my 1070 in the horizontal position IF the fender allows clearance to use a chain hoist attached to a high beam. The chain hoist allows vertical precision and the high beam allows horizontal swing. Getting the chain hoist perfectly vertical for disassembly will allow one to work gently with the seal during assembly and do it without a helper. Being creative with bungie cords or cinch straps to gently pull horizontally may help.
Also, I would consider if the extra 3/8 inch would allow me to install the seal very first and push it on the extra 3/8 inch. This would require being able to tap the OD of the seal into the hub AFTER adjusting the bearing end play. This may not be an option.
There is a saying that I remind myself of often. The pain caused by doing it right does not linger near as long as the pain of doing it wrong. Good luck on your endeavor.