its good you will be putting in a lot of pre season scouting for sheep.
keep in mind that there will be a lot of local to montana also out there before first light on the opening day.it will be a real cluster and your odds that you get to a nice ram before anyone else will be low .

if you do well hiking up for tahr you will do just fine climbing hills over here. i had a friend from nz come over this last elk/deer season and he did just fine and got use to the thinner air pretty fast
we were after elk from 7000-8500. take you time and you should adjust to it just fine but it does shut some guys down pretty fast .
what are your dates you plan to be here in mt ?
if you are planning on doing any other hunting while here like elk/deer
i am sure i could help point you in a few areas that have both
also be handy with those longer shots if it come up . this kiwi in my elk camp had never shot past 400yrds before and on opening day i put him on a group of elk and 1 very nice 6x6 bull at 578 yrds
and he passed on it and just took pix for about 10 min before they went on there way.