Wow, I thought the rim size made tyre selection limited for the 800! 120/80 is very unusual.
I doub't youd have any issues going with a 70 profile instead. It's what
@Lord Farquaad apears to have done with no reported problems.
I highly reccomend the Metzeler Z8 interacts. My favourite tyre so far, over their whole life.
My favourite (now ex) Ducati dealer Lincoln, reccomended them without hesitating when I asked and they wern't wrong...
I've used the MT60, the Z8's & Bridgestone T30's on Scramblers. Pilot Power 3's & Metzeler Sportec M7RR, Dunlop Sportmaxx & Pirelli Diablo Rosso 2/3's on other bikes.
Z8 remains a fave and definately the best I've used on the Scrambler. The T30 is ok but when new it's very egg shaped, likes to drop into a turn really fast but gradually wears to a more liner turn.
Z8's felt the same from day 1, until they were almost dead. Really nice linear roll onto the edge too, much like the standard MT60, except they last twice as long and handle way better. Livens up the scrambler, as I supect they are much lighter than the MT60. Being a single compound, Metzeler reckons this makes them much more even in feel across the profile, no changes in grip or feedback. Maybe thats why I like them so much... best compliment is that I didnt think too much about them, until they were gone.
Local bike tyre guy swears by Continental Road Attack 3's though. he tries just about every tyre that comes out but keep's those on his main personal bike. So I'll be trying them next.