If they are actually R-1 Ag tires, the hubs may be movable. See if your hubs are bolted to the wheel rims. If so, look on the inside of the wheel and you should see the provisions (brackets with nuts welded to them, IIRC) to remount the hub for a different offset.
If your hubs are welded to the rims, you may be able to swap the wheels side to side (can't just reverse them as Ag tires are directional), but measure the offset on the inside and outside of a wheel to ensure it's a worthwhile swap.
This is from the 4005 (your 970 is the 4005's grand daddy) operators manual:
Rear Wheel Positions:
• WIDE POSITION - Install wheel with valve stem to the outside.
• NARROW POSITION - Install wheel with valve stem to the inside.
The mounting flanges on the rear rims are closer to one edge of the rim than the other, allowing the inner wheels to be mounted in different positions. By changing this position of the wheel on the rim, up to eight different tread widths can be achieved on some tractors.
BTW, if you have the Operator's Manual for your 970, widening the rear track is explained in the manual.
How much clearance do you need? Have you figured that out yet?
ADDED: on my wheels (turf tires, BTW), the WIDE position has the valve stems on the inside. I'm wondering if those instructions above are an error in the manual. Anyway, definitely measure the offset before you do anything else!