Will a 35x13.5 or 37x13.5 or 12.5 on 20x10 rims fit on a stock

[Synn]

Will a 35x13.5 or 37x13.5 or 12.5 on 20x10 rims fit on a stock h2 with out mods

Yes I have read 35x13.5x20 will fit ...Any mods needed

And with the 37x13.5x20 tires ?
1) I have heard they fit but do gears need to be done ...will it die on hills

I have done searchs and find different answers to this questions because are just happy they fit but they dont mention other decideing factors like needing to do gears and such

Thanks

Lee