I dont know the offset for the spare but the issue youll run into is more than likely youll need to buy new tires. for the spares. its the most neglected tire on any vehicle.
IIRC, the compound used for most spare tires is a softer than normal compound that doesn't age and dry-rot, but it also wears faster. I think the colored stripe in the rubber has something to do with it. IE, I think it's a blue stripe on our model years; it's actually blue rubber molded into the tire.
The tires should be fine but they aren't going to last 60,000 miles.
Last bit of anecdotal evidence. About a year ago my parents got a flat on their '94 suburban. Catastrophic flat that couldn't be repaired. The original spare was still aired up, in good condition with soft, pliable rubber from 23 years prior. They put it on and drove a few thousand more miles until they found a good match to go with the 3 remaining of their tires. They put the spare right back in the spare compartment with complete faith that it will continue to live on.
I can ask my FIL; he makes tires...
